I'll admit that I much prefer the pre-2015 installation process because I can keep copies of the installers, serial and registration codes locally and reinstal on any PC capable of running Sonar even if Cakewalk the company no longer exists. I also have severe doubts whether Calkewalk could, as a final act of the company, remove all copy protection and make the installers a free download as Cakewalk staff have indicated on this forum. It would depend on the circumstances.
I don't know about the US, but in the UK if Cakewalk/their owners went bankrupt the software code and the possibility of charging for support would be regarded as a highly valuable financial asset by the reciever in bankruptcy. The reciever would be running the residual company, seeking to maximise its value so that the maximum possible can be paid to creditors, either by realising assets or selling the company. The owner (or staff) simply giving away a potentially valuable asset would not be allowed, and if the asset were given away at the point the company was clearly bankrupt but had not yet sought the protection of bankruptcy the owner/staff might find themselves in a great deal of trouble.
Having said that, the only alternative to Sonar I can readily see myself using is Logic Pro, and exactly the same situation arises with Logic as well. So I've just bought Sonar Platinum anyway.
I guess the safest answer is to not only back up projects and audio data but to also export all MIDI stems so that the project can be recreated, as far as possible, in other software if required.