User blog comment:Ltmaroon57/Maybe Summer Is Alive?/@comment-4010415-20180831005902/@comment-24934890-20180831170810

Anime101: Don't believe a character is dead unless they are seen dying.

Or heck, that could be applied to fiction in general. We all thought Ozpin was done and gone, but NOPE. In Fairy tail,  everyone thought Lisanna was dead but NOPE. Heck everyone even thought Jellal was dead, but NOPE.

In Dragon Ball, everyone thought Goku was dead after his fight with Frieza, but NOPE. Now think of all the characters we saw die in fiction. We know for a fact that Pyrrha is dead, because we saw her die. We didn't see Summer die. So far, nowhere in the show was she stated as "dead." It's implied that she went MIA, and her family thought she was dead.