The window is definitely not closed after this season, but Hedman's play could be a concern moving ahead. He just turned 32, so I can't believe he's already declined to this level already. As far as next year, provided Hedman is still capable as a 1D, the biggest decision will be whether to focus on all the forwards and Cole/trading for/signing another 3LD in the offseason, or going after a top 4 upgrade on defense. With Colton, Jeannot, and Eyssimont needing new deals, plus a decision on Perry, that would probably eat up at least 7 million in space(being conservative). Right now, with 7F, 7D, and Vasy signed, the team has 9.25 available, counting the dead weight of Myers and his 275k buried hit and a projected increase of 1 million. If Myers and one of Fleury/Raddysh are subtracted, that leaves approximately 10.3 million for 7 signings in order to reach 21 players.
A backup G, whether it's Elliott again, Alnefelt, or someone else, will be 850-900k, so now there's tops ~9.5. If JBB pulls some magic and gets the 3 rfas plus Perry or another 4th line vet for 7 million, that leaves the team with at best 2.5 for a 12th F and a 3LD. I can't see Cole returning in this case, but one of the names on that list could probably be had for 1.5ish. Tampa would then use the remaining 900k-1 million on the 12th F.
JBB could decide to move Colton+ for an upgrade on defense in a hockey trade, or an even more surprising move with Cirelli for an even better dman. In any case, there's just no room for both, so either he signs all the main F's and keeps that group as strong as possible while banking on Hedman, Serg, Cernak, Perbix, Bogo, new 3LD/#7 acquisition and one of Fleury/Raddysh, or he sacrifices one of Colton or Cirelli to upgrade the defense(I suppose Jeannot could be moved as well, but that seems very doubtful after what JBB just paid, and Jeannot will likely save the.least among any of the possible F moved).