Max's arc is a coming of age story based around a special friendship. As mentioned elsewhere in this thread, those stories typically end with the special friend dying in some horribly poignant and sad manner. Being saved by time travel and then killed by time travel (in those circumstances) fit's like a glove. Coming of age stories don't end with the protagonist trying to kill themselves, so you're view of what happens next to Max is one that clearly doesn't match the writers' intention.

Chloe's arc is one of going from a person who is defined by what she hates to becoming a much nicer and more pleasant person. It's a redemptive arc. There is no greater redemptive act than to give up everything you want so hundreds might live- especially when you remember that Chloe feels that the town wronged her. As for the sacrificing Chloe- it's not even an option until Chloe pulls out the butterfly photo and tells Max she can do it. If she really didn't want to sacrifice herself she could have kept quiet about having the photo. But the point of her sacrifice is that, yes, she didn't want to die- if she did it wouldn't be a sacrifice. She decided that being sacrificed was the right thing to do and chose to give up what she wanted in order to do it. The ultimate culmination of that arc.

Those are the arcs the writers wrote for these characters.