It's fun (or not fun) to value trades this way but it is all built into the process. Whether or not Sanchez has a 0 WAR career or a 15 WAR career will allow us to look at the deal in hindsight, but right now, it's understood that either thing is possible and he had considerable value. And they still thought the short-term gain was worth it.
Harder to value the re-signing factor - I think it's true that the Phillies do not view this as a two-year acquisition. If Realmuto doesn't hit the open market (unlike Lee though he also wasn't even on the Phillies at the time) then having him in hand clearly added some value, even if the discount isn't steep. In Lee's case he was not in hand and there was no discount though obviously his familiarity/sentiment, and the Phillies' ability to land him, was based on his previous experience.
(btw I have seen several articles lately saying that Cliff Lee turned down more money from the Yankees to come back to Philadelphia. That's not how I remember it).
My guess is the Realmuto trade will look a lot like the Lee/Indians trade. Alfaro will probably have real value, as Carrasco has (after a few bumps). And Sanchez could have the career that Knapp never did. Or the same exact outcome. If Knapp had become an ace I don't think we'd regret the Lee trade in hindsight (we just regret the Phillies trading him).
Revisiting the Lee trade and the Oswalt trade and even the Pence/Victorino sales just reminds how cheap and luxury tax-averse that ownership group still was. The 2012 and 2013 non-rebuilds still could have worked if they'd been willing to spend the money instead of trying for stopgap fixer-uppers (Delmon Young, Revere, Burnett - who wasn't even cheap!) as Howard, Lee and Halladay declined but were still on payroll.