Besides, Slott and editorial can come out and say "Yes, this is Mayday, it's permanent, ETC, ETC" but there's not a damn thing that stops a future writer and editorial team to come in and continue Mayday's adventures, ignoring Spiderverse completely.
You see that with death in comics all the time. A writer and editor will kill off a character, say that it's for real and the character will stay dead... only for a another writer and editor down the line to reverse the decision.
Considering how many people grew up with Spider-Girl, it would not surprise me at all to see someone undo Dan Slott's story in the future if they break into Marvel Comics (lord knows I would).
Hey, this whole universe was started with the question, What if?! So sure. Maybe one day.