Likely accept that worst case switch the 7th to a 3rd worst case

IF they can't turn it around then yes. Tampa shouldn't trade Perbix though.

Also odds of them retaining for 2 years is low

Dude has Perbix derangement syndrome

No retain and we have a deal

Gotta retain to make it work cap wise

Agree with Seattle not retaining for 2 years, but dude Perbix's start to the season was tough. A wet napkin might have been more effective to start the season than he was.
He might be playing fine now but it's no secret the guy is nothing more than a 3rd pairing defenseman on a cheap caphit getting glorified for getting carried in the top four last year.

To answer the questions you posed in the title:

1. Seattle appears to hold Borgen in high regard and really values what he brings. They were patient with him and gave him his chance to be a full-time NHLer, an opportunity he seized. They are also in a position where they're likely going to be retooling a bit this deadline, but with an eye towards competing again next season. Borgen with his contract and role would likely play a decent role in said turnaround. With all that in mind, the Kraken may be willing to trade Borgen, but I believe in order for them to do so it would take an offer they cannot refuse.

2. The value isn't bad in my opinion, but I think it's still an underpayment by the Lightning, especially if Seattle would be retaining half of Borgen's cap hit. I think a more even value would be Borgen for Perbix plus a second round pick and fourth or fifth round pick, but when factoring in the retention and the fact that the Kraken aren't especially motivated to move him, it might take something along the lines of Perbix and a first round pick to pry him half retained out of Seattle.

Sure but he's still young. The solution should be to add a defenseman to push him down to the 3rd pair

Ideally yes but part of that issue is we don’t have the prospects or picks to get a solid enough RHD. Perbix will likely have to be used in a trade to get someone better.

I mean we are probably looking at a pure rental because without double retention we likely aren't getting a top 4 caliber guy

you do realize jack thompson exists right?