You could probably find out the migration status somehow from the temporary files that cvs2git leaves behind. But you are trying to solve your problem at the wrong level.
Instead of running cvs2git in a straight ssh session, you should, for example:
Redirect its stdout and stderr to files, which you can view whenever you want:
nohup cvs2git --OPTIONS ARGS >cvs2git.out 2>cvs2git.err &
Run cvs2git within a screen session.
screen
(1) is a very handy program that allows you to detach from a terminal session while it is still running and reattached to later, even from a different computer. (It can also do many more things, like allow you to run multiple terminal settings through a single SSH connection.)