On average for Fortune500 companies the standard multiple is around 15 times earnings. x20 or so times for Technology. Granted these likely are the dominant player and are much more stable but Saas companies have growth potential that likely exceed such companies.
I think the 4x earnings upper limit is extremely low, especially as there is likely a reason they are trying to buy you out, not just from keeping it relatively stagnant in terms of development and collecting profits. I think at a minimum x10 earnings for a substantial Saas would be the low bar estimation by me.
Lets be reasonable, otherwise you would just hire someone to maintain and just cash in if we are talking about a company like this article is talking about.