VFR :
I'm not convinced there are limits for negative G. Personally, if I ever got there I think the most important factor in deciding whether to get down on the ground would be the strength of the resulting smell in the cockpit.
Seriously, my tactics are 1) avoidance, 2) aft cyclic to reload, 3) DEEP breath, and finally 4) probably put the thing down immediately under power to reduce exposure time if the mast has been bumped because if I get past (1) I'd be a test pilot without the CV to back it up.