I can understand the sake of ease for stating Opt IN vs Opt OUT but does that not specifically state they they want nothing to do with the instance at all? In a word perhaps ignoring that it is actually happening? As to me wanting to Opt OUT would mean you want nothing to do with being harmed or having something happen to the character which can in a way build the character as well, or add more avenues of RP.
This in a way to me not wanting anything to happen to your character without your say so (Maiming, scars, mental physical etc stuff like that) is essentially god modding. Now I'm also presuming the party with that intent as informed they are doing XYZ. I am also fine with that hey they did XYZ but you were able to get a regenerate cast on you in time to leave no actual 'marks' by all means that's a fair compromise. But just to say hey ya you can do this and then have nothing to show for it? Be it mentally or physically is disheartening.
This should be understood as a possibility of happening in DM events, you never know what may happen. PCs can escalate certain instances on their own by this or that decision or action. So in a way you are telling the DMs who are attempting to help create XYZ story for you how to go about doing it if your char is involved.
I'm sorry but this is just a medium of PnP and if your char decided to barrel into a small room and decide to cast a large volatile spell at the monster? That DM is going to set the obvious actions in motion, cave ins most likely being the case, backlash etc. (saying you are underground)Say your character got a rock dropped on their arm, say crushed? Regenerate may be cast or you did not have anyone able to do it soon enough? To me you should have quite a bummed arm, or something which would denote you just had a hell of a time. You should not come out of that unscathed whatsoever. Now to some this may be an extreme case, and these are just my thoughts I am not forcing my RP wants upon any just giving my 2 cents.
In cases where I have say put down a char or something and find out later they are back alive or look as if nothing happened? I bite my tongue, unfortunately I have to as I cannot expect others to RP as I may.
Anyways! Hopefully this is not coming across too harsh or badly worded, I just wanted to throw in some cents.
(Also I am fine with being on the Opt IN list or whatever Slunko, even if others may believe it a poor reason for your char and there are other ways to RP. This is the route of the char and you've stated that you're open to it changing with the RP portrayed be it he being dropped or someone finding another way. )