@Carnival-Boy said:

But it's about doing your own cost-benefit analysis. It's too simplistic to say you should never run legacy applications.

Of course, there are always times that legacy applications need to be run. But there are limits too. ASP as a platform has been legacy for a decade and a half. That's a long time. It has a pending end date for when it may not be available any longer in any capacity. It presents platform level risk which may prove to not matter, but may prove to be extremely limiting in the future - that's the nature of risk, we don't know what will happen with hardware and software down the road. But it is technical debt building up in a platform that is nearly all of the way through its "trailing off support" timeframe.

It's fine to have legacy apps. But it is also important to identify when a legacy app is becoming too legacy. In the OP's case, ASP created support and hosting risk in addition to normal concerns. Those were probably types of risk that were not considered in the past. Any business running ASP is constrained if they decide that they want to go hosted, for example. They might not ever decide to do that, but there is technical debt potentially making that decision for them, as well.

Any ongoing support of an ASP legacy app means that investment is being put into the old system. Maybe that is trivial, maybe it is major. Technical debt is a hidden cost. Money goes into keeping the old system running instead of being implemented in a new system. The effort to support the old could offset the effort to replace it.