MacOS stuck decrypting

I have researched this a lot and managed to stitch together lots of different answers from here and SO but as Windows dev I am not that familiar with the ins and outs of Mac.

I have (had) a 2012 MacBook Pro (High Sierra I think) which one day failed to boot. The progress bar got stuck at 99% on start-up with lots of fan noise etc. I left it for days and still nothing. I then started following threads on this forum and tried an Internet recovery which began to reinstall but then failed with errors that were hard to diagnose. I had triple checked before I did this that an in-place reinstall wouldn't lose any personal data that was important to me. Naturally I don't have a recent backup. What happened after is a bit hazy. Unrelated the mac's battery exploded so I removed the drive from it and have connected it via usb to a new MacBook. using disk util I can see a large external drive of nearly 500gb with no partitions, an unknown format and about 2.5GB is used space. I ran first aid and no problems found. I tried a data recovery tool but as the disk uses FileVault it obviously found nothing. I followed the instructions on here to begin a FileVault revert/decrypt using terminal which started slowly, it got stuck at 68% for a day or so, but eventually started moving but is now stuck at 78% after nearly a week(!) - Simultaneously I have run Stellar data recovery and this can "see" loads of my lost data, so I presume this is on the now unencrypted 78% of the disk. Aside from waiting for another week, are there any logs I can check on the status of the decryption, or alternatively anything more fundamental I am missing on recreating the seemingly missing partition(s) that would natively give me access to the data that must still be on the disk (as Stellar can see it)?? Any help gratefuly received.

(My first post was better constructed, but it refuses to submit to this forum on a Windows machine, so apologies for any grammar issues here)