It's highly unlikely that Vettel will walkout his Ferrari contract mid season for anything other then instant retirement. As a driver under contract you just can't do stuff like that and for Ferrari it would be very unwise to designate him as a scapegoat.
As for Albon, I think he performs as expected. He wasn't brought in as a challenger for Verstappen, he was, for 2019, someone they rang up to fill a Toro Rosso seat because they blew trough all their juniors. The last seasons Verstappen on the other hand showed perfectly that he excels without added pressure from the other side of the garage. In other words, he needs support, not a push. So far this season, Albon's point scoring was perfect, one place behind his teammate, in quite possibly not the most predictable car at the moment. That Honda still making the back twitchy on the apex.
As for Vettel, how much I like him, somehow those nine victories at the end of 2013 changed him, almost trying to get that same invincible magic feeling back but never finding it. If you've done perfection, where do you improve? Like his switch is still stuck there, and should be turned back to 2009.
As for Sainz, you don't want to hop in a difficult Ferrari mid season, look at fisi.... Having his dream at the back of the grid and ending his career.
I expect that Vettel takes a sabbatical just like Hakkinen did...