No more perpetual Framemaker Liense? Looking for alternatives

I don't think the OP was saying that the new subscription model would impact their already existing perpetual licenses; rather the concept that if you stop paying, you lose access to your docs through that software. It's a bit like looking at the "total cost of ownership" on something - is it cheaper to rent or buy something outright? With the direction of going subscription-only, you get forced into the "rent" model.

Something seems unclear about your question.

A perpetual license is something you pay for once, and can use as long as you have a system on which you can run it. So why would the new model prevent you from using what you already have?

Monthly subscription means you get all the latest features, but on the other hand you are dependent on your company being prepared to pay this every month.

One might ask if anything is really "perpetual" when it comes to software.

I have a perpet license for FM7 from 2002, probably on Win95 at the time. It was migrated forward to XP. Then XP itself had to be run in a VM on Win7, and now Win7 is too dangerous to run, other than air-gapped, which I don't, largely because the lack of Unicode support in FM7 is becoming a serious annoyance, which leads to another insight:

Unicode support isn't a feature. It's a process.
FM, as of 2020, still doesn't support SMP (codepoints above U+FFFF). It's likely to happen, but you'll need to be getting the updates for it. We could also discuss the elegance of the combining characters renderings. Even so, Unicode itself is in continuous flux, as are the various industry document delivery standards.

If I were still in tech pubs management, I would be keenly interested in solutions offering portability and open-ended stewardship. In addition to concerns arising from needing to maintain the subscription, you can never tell when a supplier will sunset a product, close up shop, or get sold to a new owner who will discontinue the product.

I might also opine that Adobe has to have a licensing solution for their customers who are air-gapped for security reasons other than Microsoft EOL.

I'd like to see Adobe offer all of their products as cloud services, with short and long-term term rates.

I'm not particularly happy with the subscription model, myself, and for that very reason.

On the other hand, if you run the numbers you'll discover that it's cheaper, year over year, to get the subscription rather than pay for a perpetual license, especially if you expect to keep upgrading versions. The subscription works out to $360/year, give or take, and includes upgrades to any major version that is released during the subscription period, and my recollection is that even an upgrade to FM was close to $1000 each time. (My recollection may be faulty, given the last time I purchased one was for FM2017.)