Have not done an edge but patched a hole caused by an errant jack cylinder. Can't speak exactly for yours but mine had a plastic sheet on bottom to seal, Styrofoam next then the OSB on top. I squared up the hole, slipped a sheet of very thin aluminum (beer or soda can) between the plastic sheet and the Styrofoam, filled the hole to the top of the Styrofoam with aerosol foam sealer from Home Depot, leveled it with a hand grinder and topped it off with a plywood plug epoxied into place.
You should have support on the edge of the OSB. Catching two edges of this with plywood will provide some strength. If you can peel the OSB off the Styrofoam, then bond the plywood back on it you will have quite a bit of strength from the Styrofoam. you might also be able to use a biscuit joiner, dowels or pins (cut the head off of 16p nails for these) to attach back into the remaining OSB. Use lots of epoxy such as JB weld.
Never say never. Good luck!
