Good question. That’s not something that I have ever done i.e. I’ve always booted Jumpdrive, done what I wanted to do, then rebooted normally. So I don’t know whether there is any kind of time limit.
The obvious thing to do would be to boot Jumpdrive again and see whether the phone again operates correctly (in Jumpdrive).
I would suggest again though: boot Jumpdrive, make a disk image of the entire eMMC drive onto the host computer, then shutdown the phone. Then you can retrieve files from the old contents of the phone now and forever (by using the disk image). You will of course need approximately 32 GB of free disk space on your host computer in order to use that approach.
(I assume that that is just a typo when you have transcribed the error message. Should be mmcblk0
.)