But actually there is no notification that the license is expiring or has expired until you release a new upgrade. So if my license expires today for upgrades and you don't release another upgrade for 45 days, there's no way for me to know that I missed the 30 day window.Actually, it costs $49.50 per year if you prolong your subscription within 1 month upon termination. If you do it later (say, in 6 months), then, yes, it will cost you $89.50, because you will get the upgrades for the past period (that 6 months) and one year since the prolongation date.
I'd suggest that you make the $49.50 price be for 30 days after the upgrade following expiration. That way, when an upgrade is released, a customer has 30 days to renew and get that upgrade.