I think there are more ways for the deal to work out for the Nats with the trade than without it (reversing it). We got a premium from SD because they are in a playoff race, so we'd be giving that up. The Nats need a couple of guys to be major pieces, but there are a lot of ways that can happen.
If I could keep Susana for Bell, and you told me that we'd sign a premium SS this offseason, I think it would be a closer call. Meneses would be at first, and we'd have essentially Soto and a Trea-like SS in 2023. Easier to augment that. OF FA would be needed, but not a big signing.