[rawgabbit]

Your leadership will view the situation from a Risk-Reward lens. They know the reward which is the revenue it brings in. They will ask you what is the worst that can happen and then they will decide to continue or shut it down.

I personally think that lifting and shifting to Azure is a good thing. Next you should get Microsoft Premier Support/Premier Field Engineering to analyze what you have. They will give you plan on how to improve reliability and probably reduce your costs as well. You take that plan and explain to your client the good news/bad news. The bad news is that Microsoft says we should perform the following to improve reliability; the good news is that your company will not charge the client extra; you will improve reliability for "free". As reliability improves, your company can direct the senior devs to start designing version 2.0 (maybe).