So which defenseman does Dallas lose in the expansion? Lindell, Klingberg, or Heiskanen?

Karlsson is a nice short-term addition, but I guarantee he's not coming without a NMC, meaning the Stars will HAVE to protect him. It really screws Dallas in 2 years when they lose a piece of their young defensive core.

OUCH!

Exactly why the only notable top-4 RD the Stars should target this offseason is Anton Stralman. Give him a 2-year deal and then by the time the expansion rolls around, his contract is over.

The other short-term solution is to trade for a RD. Teams that may be dealing with Cap issues would be the ideal choices. Assuming they sign Karlsson, trying to get Braun from San Jose is a target. You've also got Colin Miller in Vegas and Matt Niskanen in Washington that could be solid short-term fixes. The expansion draft is really going to change how teams approach the next couple of offseasons.

If they can't make a deal to have someone else taken, it's Lindell

And if you're Seattle, how good does the deal have to be for you not to take a defenseman that would instantly be your top-LD and a young cornerstone to build the rest of your defense around? Dallas would have to give them one hell of an offer to keep them from taking any of those three.

I think you hit the nail on the head with these two statements.

And that is still a bad option for Dallas. All three of those guys are keepers. Where is Ollie Maatta when you need him?

The only other scenario is Lindell taking a 2-year contract this offseason (he's a RFA), and I can't see him doing that. He's played so well over the last two years, and is playing insane minutes every night. He's looking at a 6+ year deal and I can't see him risking 4+ years of top-pair money just so Dallas can sign another defenseman.