In an incident like that, if you don’t have a helmet on you can pretty much guarantee being screwed. If you javelin yourself into something like that, you’d probably have some kind of neck injury either way, helmet or not, but with one on you would help prevent leaving your brains all over the side of the car or other object you hit. Having one on also protects you from the other randoms that could happen. If you hit a slick spot on the road in a curve and lowside you have a pretty damn good chance of at least bouncing your head off the pavement when your body hits the road - if you have a helmet on what’s the chances of splitting you noggin open? What are the chances if you don’t?
Don’t beleive me - try this. Put a helmet on, go out into your street, get on your knees and just slam your forehead into the road as hard as you can. Now take the helmet off - repeat. Tell me which hurt more. (Go the the ER first and get some stiches - wouldn’t want you bleeding all over the keyboard). Guess what, that was a 0 mph lowside - want to try it again at 35 mph? You want to know how well other gear works, take a running dive in the same street. Tell us how well your jeans and T-shirt held up in a 7 mph slide. Hell, I even have some old gear here someone can use if they are serious about trying it.
Quite simply, if you like your brain being intact, wear a helmet. If you like your skin, wear the gear. If you just want to look cool and don’t give a shit, do what you want, but expect criticism not much sympathy when something happens, and chances (and statistics prove) that it will eventually.