Having just about finished doing mine, I'd say replace, definitely, really not worth even trying to repair that -the crossmember isn't expensive, and a replacement Ali floor from an earlier Range is cheap, I picked mine up through this forum for just £15.
I actually bought, via Eay, two pieces of folded steel (into a Z,) to remake the boot floor lip, it was relatively expensive £15 each + P&P) but has make a good job of it and definitely much easier than trying to repair.
Whilst in there you'll probably need to visit the seat belt mounts on the wheel arches, the arches, rear footwells, c-pillar etc, do it right, do it once.
HTH, Along with Orange's write up I have a load of pics if it will help....