They aren't going to sign him to that. They will trade him for more draft picks and/or cost controlled RFA players and continue their cycle of surrounding their core with new fresh affordable players.
The cap isn't going up. It might even go down next year. After filling out their roster with 23 players CHI has around 2M of space this season. This is huge for them as it will cover a big chunk of Panarin's performance bonus, but they'll still be hit with more than 500k of it in overages next year. There's almost NO money coming off the books from CHI. About 800k if they replace Brian Campbell with a player on a 2 way contract. But when you consider the cap overage from Panarin's bonus, that savings is cancelled out almost entirely. So next year, after filling out their roster with a bunch of two way players they have about the same thing amount of cap space as this year assuming the cap doesn't go down, 2M in space. Panarin makes 800k as a base this year. That leave CHI still over 3M short.
In order to afford giving Panarin a bump up to 6M, they'd have to move someone making 4M or more (when figuring the cost of a replacement body at 800k for the player moved). I guess they could trade Crawford and go with Darling, but are they really going to take that risk after Crawford has provided them with stable post season goaltending through multiple cup runs?
With Panarin being as valuable as he is going to be on the trade market, I can't see them not trading him for a laundry list of useful pieces, similar to what they did when they sent Saad to CBJ. The only way they have cap space to extend him is if they get rid of one of their current core guys or if they "luck" (as awful as that is to say) into a declining Hossa getting a career ending injury and being able to get put on LTIR.
You should go back and check the cap numbers again.
Chicago has a 3.07 mil bonus overage for last year which will be removed. The Hawks are retaining 1.125 mil of Rob Scuderi's cap hit which will be removed. Panarin is already costing .8125 mil on the cap this season.
3.07 + 1.125 + 0.8125 = 5 million
If Panarin's asking price is 6 million, the Hawks need to find 1 million to fit him in. The current team is 2.5 million below the current cap - and that includes the 3 mil bonus overage from last year. So even if Panarin hits his 2.5 mil B bonuses, the majority of it won't be an overage provided that the Hawks don't use that cap space on another player.
Let's look at it a different way. The Hawks have 11 players signed and 15 million in cap space for next year, if the cap stays at 73 million. If Panarin is signed for 6 million they Hawks will need to fit in 10 players within 9 million cap dollars. Difficult but certainly doable considering they will be filling out bottom 6 forwards and 5-7 defensemen.
Another possibility is Kruger leaving via the expansion draft or through trade.
The point is 6 million is very doable for the Hawks and, if this rumor is true, for Panarin.