If the best Dillon can get on the market is 2.5M he'll just stay in Winniepeg. The max term you can give Guentzel is 7 years

In this scenario they paid a fourth so they could give him the 8th year

not how that works. Carolina would have to sign him to an 8 year deal first

Yeah seems like Dillon is interested in staying with Winnepeg, but I haven't seen anything showing they're planning on re-signing him just yet. Maybe he would be convinced to play at home. Also Guentzel would be a sign and trade for the 8th year, otherwise yeah it'd be a 7 year deal likely worth a bit more AAV.

The reports are Dillon wants to test the market actually, but 2.5M is a weak offer for him. It's been reported as well that this will be a very good UFA year for defensemen in terms of getting paid.

As for Guentzel, I'm assuming your comparison is the Severson deal. IIRC they traded a 3rd to new Jersey for Severson to be pre-signed. That was because Columbus wanted to basically skip the line on July 1st, but also because New Jersey had no intention of re-signing Severson due to cap reasons. By all reports Carolina wants to keep Guentzel though and have the cap space to do it

Honestly I think VAN is better served saving the 9M on Guentzel. Take that money and spend on filling out the rest of the FWD core. Maybe go for a guy like Toffoli at a lower number.
IMO this FWD core is top heavy and Van would be better served creating 4 deep lines. Petey, Miller, Boeser are all guys that will score at an elite pace anyway - not like they are lacking firepower in the Top6.