I think with the RP/Aston thing there's too much assumption that Stroll won't be dropped. His dads a businessman and he has a large board of directors and a historic car brand to keep happy, and he'll know when sacrifices need to be made. Aston Martin wont settle for sub par line ups when there is great talent out there who can prove their worth and are doing so.
Mad predictionz:
Hulk and Vettel confirmed to Aston Martin for 2021.
Perez goes to Alfa Sauber, former FDA driver and former Sauber driver, can take good backing to a struggling team. Giovanazzi isnt secure, if Ilott/Schumacher/Schwartzmann win the F2 title. So let's say Perez and Ilott for Alfa.
Stroll wont get dropped by RP/Aston/Dad without some sort of security for his F1 seat. Discussions I reckon will already be at full steam for a deal with another struggling team, Haas, for Stroll to go there with an injection of 'sponsorship' money to replace Magnusson or Grosjean. Haas want to stay in F1, especially with the looming budget cap, they also want some cash to come in. They've yet to confirm their drivers I belive. I don't think either can feel secure, whoever Stroll would replace, I think coukd be alonside another FDA driver who can bring in some extra backing. Schwartzman would be a good shout there.
Summary.
Aston Martin - Vettel, Hulkenberg
Alfa Romeo - Perez, Ilott
Haas - Stroll, Schwartzman
Massive long shot but I predicted Sainz to Ferrari, Alonso to Renault, and last season Leclerc to Ferrari, all well ahead of any announcements. So don't rule it out just yet.
Yes I know it probably won't happen.