If LibreOffice ceases to exist, won't the old installers still work? Is it forkable to a new project? I seem to remember that it was Star Office then Open Office then LibreOffice.
I think such situations are rather big risk that a community that already wasn't very active atrophies or splits and then atrophies. With code bases like that there's also a lot of maintenance so being able to run an old version is not necessarily enough.
What maintenance are you talking about? I'm quite sure I could open any document on my computer with a libreoffice version from ten years ago. The functionality doesn't magically rot away...
The questionnis: How does a community form, which can take a project tof that size? TDF andjvre Office cMd out of a long process of independent (from Sun Microsystems) contributions to OpenOffice, which at some point had a momentum to do a proper form and then another momentum to take over as the lead variant.
For a successful fork you need a notable amount of people engaging in the fork.