Well let's see...
Based on the current roster, the Stars have $90,176,666 committed to the cap in 2025-26, which is $5,323,334 in cap space on a roster of 16 (8F/6D/2G)... to fill out a 22-man roster (13F/7D/2G) they need 5 forwards and a defenseman and would only have $887,222 for each of those 6 roster spots.
As other have mentioned, Dumba will be gone. At a 3.75m cap hit for 1 year and 3.5m owing, I can't imagine it costs more than a 2nd to dump is contract.
That makes things much more manageable and would have about 1.295m per player for the 7 to fill out the roster.
I also think it makes sense to move out Marchment's contract as it would make adding depth so much easier.
Of course, Seguin's health also could be a factor. If he's done, then I don't think they have to move anyone (but I think thy woud still move on from Dumba)
I also think Bourque will be a prime candidate for an offer sheet.... not only will it be extremely difficult for Dallas to match, but he's likely to get considerably more money and playing time elsewhere.
If I were the Flames GM, I would offer Dallas our lowest 1st and a 3rd for Bourque as it'd be more than they'd get from an offer sheet. and I could easily see a team offer him 2 years with a 4.5-5m AAV, even if he isn't worth it right now because they'd gain his RFA rights for after the contract, when he may be worth the QO.