Crazy but IMO actually sensible deal if the Red Sox want to dump salary:
Sale + Vazquez for Grandal + Keuchel + Lopez + Rodon + Mazara, pre-nontender deadline
Why for Sox: They are probably looking at trying to dump Rodon and Mazara anyway, and probably looking at least at a change of scenery deal with Lopez. They effectively swap out Keuchel's spot and contract for Sale's, meaning that there's more risk and more money, but way more upside also. Vazquez slots in at C and Collins sits behind him. In reality, Vazquez is an upgrade over Grandal as a C immediately, and he is under control through 2022 with also a chance at a QO if he is worthy for 2023. Grandal is guaranteed through 2023 so it's almost a wash on control, and Vazquez is more easily extendable for 2023-2024 because his current contract basically would mean that the Sox have him by the balls a bit. I bet Hahn could extend Vazquez's deal.
Why for Red Sox: They get to dump all of the remaining salary owed to Sale. Also they can choose whether they want to try to take a shot on Rodon as a SP or closer as a deadline piece, and a shot at Mazara also as a deadline trade piece. Keuchel gives them rotation certainty at a much more reasonable cost and Grandal really fits the Red Sox as a part time C part time DH with OBP and power. Lopez is also a reclamation project they have rotation space form, but one they could try to keep if they can fix him. If the Red Sox wanted they could nontender everyone but Keuchel and Grandal.
Not sure on arb raises but in 2020 salary the Sox send out 18.25M for Grandal + 18M for Keuchel + 4.45M for Rodon + 5.56M for Mazara + 0.605M for Lopez = 46.865M in 2020 salary, and send out 110.75M in guaranteed obligations to Keuchel (56M through 2023) and Grandal (54.75M through 2023). Meanwhile the Red Sox send out 30M for Sale + 4.2M for Vazquez = 34.2M in 2020 salary and send out 142.25M in guaranteed obligations to Sale (135M through 2025) and Vazquez (6.25M in 2021 with a club option on 2022 for 7M with a 0.25M buyout). The Sox would take on about 31M more in guaranteed money but would get Sale through 2025 and Vazquez through at least 2022, again with a great chance of keeping him beyond that point.
Personally I would chance it with Sale if the medical staff and pitching coaches could look at him. The contract lessens in value over time, down to 27.5M then 20M in 2025 for his age 36 season. We would be betting on a successful return from TJ and paying for his age 32, 33, 34, 35, and 36 seasons, probably hoping we get some help in the second half of 2021, an ace in 2022-23, maybe a #3 in 2024, and a #5 or reliever in 2025.
**Edit: I like this deal because it redirects 2 contracts that I think are going to be at least somewhat regretful in 2022-23 anyway, and allows us a chance to put a legit #1 and a LHP at the top of our rotation (again) while making a defensive upgrade at C for our playoff window. And hopefully it would keep enough salary available to still go after Stroman/Bauer/etc. this offseason. I really am not a huge fan of Grandal behind the plate overall and as a leader of the pitching staff and defense, and I also don't like him taking DH ABs from Eloy who should be there now and Abreu who should be there pretty soon. And additionally I still think Keuchel is more likely to be a #3-#5 than the top-end guy he pitched like this season, and the guy who once won a Cy Young.