Do you know what kind of bamboo it is? If so, answers can be more
specific.

In any event, the plant is probably essentially undamaged and healthy.
Mowing down a bamboo is only slightly more damaging to it than it is to
mow lawn grass. If you replant large sections of rhyzome, you will
almost certainly get good results. Expect new culms in a matter of
weeks in some cases. In other cases they won't shoot until spring of
next year.

If you keep a lot of the roots intact (i.e. don't break them off of the
rhyzome), then you may do better. You are going to lose a lot of root
anyway while digging them up, but any root that you manage to keep
intact is one less root that the rhyzome is going to have to spend
energy reproducing.

Plant the rhyzomes shallow (1 inch or less under the soil) and keep
damp (though not wet).

Good Luck.

Kinda Usheq wrote:
An acquaintance of mine is offering me some bamboo
rhizomes.

Just the rhizomes because he went over the shoots with
a lawn mower. :-(

The shoots (had they actually been allowed to grow)
would have been about 15 feet (judging from other
shoots which he did let grow) elsewhere in his garden.

There should be several rhizomes 2 to 3 feet long.
Undug as yet.

If I replant them immediately is there any chance of anything
growing back? This year? Next year?