Hmmm......
... this *could* become a long-winded reply (but hopefully not!)...
I have the dubious experience/knowledge to answer both the question(s) and the next one you REALLY wanted to ask "Where can I get a roll bar?".
SInce getting my first Elan I have known (like John & Jim) a couple of people from this forum who have been shiny-side-down and gone on to tell the tale and buy another one! (admittedly, they ensured that they also fitted a roll bar to the new purchase)....
.... I was also called to attend the scene of a fatal collision involving an Elan which had flipped over and the driver wasn't able to ever say anything again

. (I had never met the owner, but had an oportunity to spend time with the family during the following weeks, so much of my 'information' was third-hand, and likely to be accurately reported).
Firstly, the Elan was (supposedly) designed to comply with all regulations relevant at the time within the markets where it was originally sold (mainly UK/Europe/USA). The winscreen surround was deemed sufficient to comply with passenger safety rules in event of a roll. Now, I have no knowledge of the engineering involved, or even the test criteria - but it is obvious that a slow /controlled roll sideways of a static vehicle will put far less stress on the structure than a higher speed dynamic 'flip'. The car will sit upside down quite happily if placed in that position, and the screen will remain intact forever. The bonded nature of the screen to the frame makes a very solid structure.... however, if the car is flipped over and lands upside down the screen will possibly (probably?) crack/shatter/break and the frame will collapse.
If you are 5' tall and can duck down, you will be far less likely to suffer damage than if you are 6'1" and slightly less agile (that's me!).
When I'm seated in the car the top of my head still extends beyond the straight line between the base of the windscreen and the top of the roll hoops - but far less exposed than without them, so less ducking down is required.
There should be no likely situation whereby an Elan will flip during normal driving - only if mechanical failure of a major component ocurrs, or Newtons' Laws of physics are applied without considering the results.
The first can't be legislated against, but proper inspection/maintenance will make those chances very small (although there have been published pictures of nearly-broken wishbones just holding on).
The second is what catches you out - and is the reason for all cases I have known (for the Elan).
If you go too fast into a roundabout/bend etc and the car slides and hits a kerb/rock/debris/other road surface, 99.9& of the time you will deal with it and drive off a little slower, possibly looking for a public bathroom or trouser shop. However, in the other 0.1% there will be no time/space/oportunity to deal with it, and you will be at the mercy of the terrain/Gods/fate as you see fit.
2 cases (one being the fatal accident) were very similar in cause - car being driven along a good road surface when it becomes necessary to move over a bit due to oncoming traffic...... once the 2 nearside wheels are into gravel/grass they will be going at a different speed to the 2 on the tarmac, steering is compromised, and if you under/over react then the physics will dictate that the car will start to spin and could go anywhere.
Graham (G-UK) ended up upside down in a ditch for a while and suffered some nasty looking injuries, but nowt life changing. Steph just went backwards into a field and ended up with a broken car.....
..... but the lovely white Elan flipped over and the driver was killed instantly - the car hit nowt else, but the screen colapsed during the flip/landing & slide. he had reacted to an oncoming vehicle which was doing a silly overtake and was in his path (not the Elan drivers' fault at all), and instinctively steered to the left to avoid the Peugeot, going onto the grass verge, which wasn't hard/flat grass - a typical English A road verge - and ended up going over. He wasn't speeding, he knew the road, he had owned the car for a number of years, he was an experienced driver.... he was unlucky!
I was asked to do the vehicle examination as I had some knowledge of Elans - there was nothing contributory to the accident. In fact, it was one of the best maintained ones I had ever seen, a fact bourne out by speaking to the family - the owner used to show it at local events and took a pride in all of his cars.
At that time, I had a set of hoops for my elan, and fitted them the next rest days! I also bought a set for my next elan (current vehicle!) and will not have a car without them (but i do travel in cars without them, so it isn't total OCD).
There are arguements to suggest that they are not great in event of an accident, have never been tested, etc etc - but knowing the designers/builders of the 2 types which were made for group buys on this forum (LGM & Kutching), I have no doubt that they are far more solid than my flat hat!!!! Both types are designed to rigidly attach to various chassis points and are made of suitable material to a high quality..... no doubt others could be made, but these are ones I trust. Both types were designed/made by people highly skilled in such areas, and I have no doubt that either would easily pass BS/TUV crash testing if submitted.
I see it as like an insurance policy - something you have and hope to never have to find out exactly how good it is. Or you can see it as a total waste of money, because you will never use it (hopefully!). EVen if it only helps a little bit, it can only be a good thing - but I don't want to test it.
....and to answer the question of where to get one - they haven't been available for a long time (but the drawings still exist) - there have been a few attempts over the years to get enough purchasers to commit to make a run worthwile, but it has come to nothing. Admittedly, i have had little interest in the process, as I don't need one, but maybe it's time for a new list and to try and get some made.....
(The ones I have were made in USA so shipping and exchange rate could well be against it now, but it all depends how much you are preparted to pay...... alternatively, there are many suitably-skilled roll cage makers out there who can do the work, but a bespoke piece is not going to be cheap).