She still would have got corrupted by that blasted Book with or without Her brother alive. Quicksilver was only Step 1 in her corruption, the bigger problems comes from losing and seeing Vision whole body being torn apart by Hayward and his Crew.

potential events for Wanda's "descent into madness"::

• the deaths she caused at Lagos.

• having to "kill" Vision.

• watching Vision be "killed" again after Vision is brought back by the Time Stone.

• being denied Vision's body.

Pietro being present might have prevented that first one. not sure on the rest.

edit:: not entirely sure, but the Avengers spliting apart might have been another potential event.

main cause for the Avengers split seems to have been the Sokovia Accords.

not sure whether the Accords would have occured if Lagos had any different outcome.

How different would wandavsion be if Pietro was still alive?

WandaVision would probably depend on the previous events of Wanda's life.

kind of still not sure, but possibly depending on what would happen at Lagos and on how the world would react to those events.

@X-Force98 Wanda being corrupted by the Darkhold had nothing to do with Lagos nor the Death of Pietro (she was way over it by 2023), it was the events of Infinity War and being denied of Vis's Body from Hayward that force her first Major Breakdown in 2023.

Vis was her Soulmate and losing and seeing him be torn apart by Hayward was the first and major Straw, all the others was small steps that didn't need to happen for her Breakdown to happen.

If Quicksilver Lived

• Lagos would've probably not happened, Pietro would be able to get the humanitarian workers out within seconds and save everyone around them, meaning no Civil War because there would be no Sokovia Accords.

• The Avengers are much more prepared for Infinity War, even if Thanos still kills Vision, Wanda won't be completely alone when she returns and would probably attend a similar therapist to the one Bucky went to in FATWS.

• Don't know what would happen to Agatha Harkness here considering there would be no WandaVision, but she might detect some of Wanda's Chaos Magic and visit her.

• Would be nice if Pietro met Crystal from the crappy live action version of Inhumans.