Yep, good points. Some sort of backup system would definitely be a good idea I think. Most people that lose mirc.ini, for whatever reason, have nothing to fall back on and have to start from scratch. I don't think a scripted solution would help much: those who lose mirc.ini tend to have no idea that that was something that could possibly ever happen anyway.
As an additional, alternative, least-resistance kind of suggestion towards making mIRC create mirc.ini backups: I've often wondered why the installer doesn't do just that. Right now (as I understand it) the installer backs up only files that are about to be replaced, but I don't think it has to be that way. In fact it would make more sense to me if the installer backed up crucial files no matter what was being replaced at installation time [*]. Having a copy of mirc.ini from before the last upgrade is probably good enough for most people in these situations, and this change can probably easily be made in the installer without affecting anyone negatively. Note that in this case, restoring the backup after a problem would be manual, but that's still a whole lot better than having nothing.
[*] After all, a newer mIRC version may inadvertently misinterpret and mess up an older mirc.ini - at least in theory, because I don't think this has actually happened yet. But this is unrelated to the thread at hand anyway.