To quote MakeMusic's blog :

To realize these enhancements, we’re doing more than merely making Finale capable of using SMuFL fonts. We’re also including updated SMuFL-compliant versions of the MakeMusic fonts that you’ve come to rely on for decades—Maestro, Broadway Copyist, Jazz, Engraver, along with a newly-added handwritten font—each with an expanded range of characters and delivered in a modern format for maximum compatibility.

Additionally, Finale becomes the only music notation software that allows for both SMuFL and non-SMuFL fonts. With this new feature, Finale v27 is set to become the leader in collaborative creation of effortlessly-readable music notation.

Given that Petrucci uses exactly the same mapping as Maestro, I'd say it is certain that you will still be able to use it. 

If there's one thing you can rely on, it's that old documents will still open as they used to. Having a back catalogue of old files is one of the main reasons for using Finale.

Read this interview with the creator of Petrucci, for an interesting take on the font.
https://www.finalemusic.com/blog/meet-steve-peha-creator-of-petrucci-finales-first-music-font/

Thank you Ben and Michel. Your comments were reassuring. Petrucci is so old and I did not see it listed in MakeMusic's blog so I was concerned. Nor did I pick up on the the announcement that non-SMuFL fonts would still be supported. Anyhow, Ben, you're right that the interview with Petrucci's creator was fascinating. I am obviously an old time user and I remember those exciting days when notation programs were first coming into being.