I'm not happy about Sonar's demise any more than you, but I figure I would have paid all or most of that "lifetime" money to some other DAW developer in updates along the way, so I'm more or less even in dollar terms.
Was Gibson unethical in making the "lifetime" offer, in view of what they probably knew at the time but were not revealing? IMO, yes.
But to me the true disaster is the time I've invested in Sonar. Some of that knowledge (the basic concepts) will transfer to my new DAW (Cubase), but not all. Not the specifics. I'll have to learn to walk all over again before I can get up to speed. If I had chosen Cubase from the start, this "Sonar is dead" thing would be just a vague rumble off in the distance.
Oh well, crap happens. I'm trying to view it as an opportunity to learn something new.
But I'll sure miss Sonar. It was a good ride while it lasted. People will be discussing and debating its demise long after the program has stopped working.