No it is not critical, it just means you need to run savebase before you reboot.
Just like it said on the screen.
Simple if you think about it.
When it says "run savebase before rebooting", what it actually means is, run savebase before rebooting.
You may have a problem if you reboot without running savebase though.
This is implied in the message, the bit that says: run savebase before rebooting.
What this means is that you should run savebase before rebooting.
So the message is posted to warn you to run savebase before rebooting.
FFS
As root, from the command line, logged in as root, type the suggested command, savebase, that's it, job done.
Nothing to worry about.
just login as root, or login as another user and su to root, then type savebase and press return.
If you get a message you don't understand at this point then please post it here and we'll offer further advice.
If you don't get any warnings or errors then you are OK to reboot.
If you reboot without running savebase, or the system hangs, crashes, has a power outage, etc. - which kind of means it will reboot without you having run savebase - then you will have a problem, probably a fairly big problem.
man savebase
for more information.
Where do these people come from?