If Bedard says "I only sign for 8 years if you give me 15 mil" then it's probably because he doesn't want to sign for 8 years and wants a shorter term. Wouldn't shock me if Chicago balked though and paid up in that scenario.
If Bedard were to sign an offer sheet, options are basically:
1) if it's 8 years, match no matter what.. now you have him for 8 years.
2) if it's an intentionally below market deal designed to get to UFA as quickly as possible, match and likely try and trade prior to when the contract expires unless you're competing for Cups by the end.. now you benefit from the cap savings in the immediate term and his "semi rental" value close to his prime if he's itching to walk will also likely be really high.
3) If it's a goofy Matthews deal with max cap AND low-term (Matthews signed 15 % for 5 years) then seriously consider taking the massive draft haul at that level of Offer-Sheet and leave the new team (that lost their draft picks) with the dilemma of best case a re-up at $19 million in five years, and worst case, he walks in UFA at that time. Good luck. I don't think any team would actually sign him to that offer sheet for the reasons above.
Offer Sheet Compensation Levels:
$1,511,701 AAV or less - No compensation
$1,5111,701 to $2,290,457 - 3rd round pick
$2,290,457 to $4,580,917 - 2nd round pick
$4,580,917 to $6,871,374 - 1st and 3rd round picks
$6,871,374 to $9,161,834 - 1st, 2nd and 3rd round picks
$9,161,834 to $11,452,294 - Two 1st's, 2nd and 3rd round picks
Above $11,452,294 - Four 1st round picks
The one really bad case scenario for the Hawks is signing Bedard to a Matthews 5-year deal where you get no benefit of more immediate cap savings and also don't get the benefit of a potential bargain on the back half in the player's prime. If Matthews had signed an 8-year extension at the same cap, he'd be at a very good $11.64 million cap hit with two more years remaining after this one and then still only due up one year earlier than his current actual 4 year contract at $13.25 million. Matthews put the Leafs in a far from ideal position, but a position that in all likelihood will greatly maximize his own career earnings.
Dubas should have never let Matthews sign that 5-year contract coming off his ELC with no real leverage in the form of arbitration rights and only being able to sign an offer sheet. We have not really seen any other player try and do that since Matthews. It's a very goofy thing to allow a player coming off an ELC to do.