well for starters main characters have died during seasons and switched over to some other side character becoming the main. it's exceedingly rare, but it does happen. there are also some series where there is no designated "main character" so anyone can potentially be put on the chopping block.
for 2, you can also do this to yourself with shows that haven't even aired yet by checking how many episodes the anime production is scheduled for. I wouldn't expect the main character to die in episode 4 of an anime that's scheduled for 24 episodes, unless it was one of those rare cases I mentioned earlier.
as for other potential downsides: I pretty much exclusively watch stuff that's done airing and it makes finding other anime fans to talk with kinda like pulling teeth. everyone's so focused on talking about whatever hype new thing is airing. the experience becomes significantly less social when you aren't watching something seasonal.