But who is saying this will be the last film? The producers have made it clear they fully intend to keep going after this, and I doubt it's going to flop so bad to make them cancel everything.
And how does one even do no Maria death? Studios have done implied, and even non-graphic on-screen deaths by gunshot wounds and explosions in other PG-rated films (Spider-Verse, Big Hero 6, even the first Sonic movie had the implied deaths of a near-entire echidna tribe and the owl mom).
I'm certainly not trying to be rude or argumentative, but I think you're tremendously off-base on this. It's way riskier for the movie to veer into a wildly different direction with a character's origin story (Hell, the whole foundation of the character) than to just stick with it. Kids have played these games, they know the character, they know what's coming. The creatives might make some alterations, they might have it just be implied, but based on how they've been true to the source material so far, it's very likely going to happen.