No, the cap is linked to revenue. The sales of the Sens won't impact revenue from a league wide perspective. Also, it's not like expansion where the $'s of the sale flow to the current owners. The sale of the Senators will go to Melnyk's estate (daughters) and also used to pay off his debts.
Now is it possible a new ownership group will lead to higher revenue for the Sens, thereby increasing the cap a smidge? Possible, but the team's appeal impacts revenue more than new owners, so don't expect any impact on the cap. For the Sens, it is likely the team will see an expanded budget to support the team going forward, as most new ownership groups invest material $s at the beginning of their tenure to make an impact.