No the "plan" is for both cities to both build new stadiums and share the Rays indefinitely.
I know, the idea sounds bonkers and it is and no one in their right mind actually believes it but that's what they're selling. It's as if they're trying to convince us that a new ballpark for a part-time team would cost less than one for a full-time team.
Actually, pretty confident that the TB stadium will never get off the ground. Looking at how long it took to actually move the Expos and all the strategems to allegedly help save Montreal (remember how we were a shared team, once, already?), TB refusing the stadium deal may well be part of the process to move the team to Montreal full time down the line.
They play in Tropicana Field for a few years and, then, when the lease is up, move it to Montreal full time...
Anything is possible. This, after all, is MLB. If something smells fishy (Marlin fishy), it usually is.