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?