BOLLIX!
IF the roll cage is made from Scaffolding (Red band) Which meets BS1387. Miminum specification for the msa rollcage (42mm nominal bore and a minimum wall thickness of 3.2mm or 1/8th) and the welding is up to scratch and the mounts meets MSA spec which is quite likley as the tubeing seems quite neat then it will indeed possibly be worth keeping the rollcage and chassis. If it were me I'd put the axles back under it properly. Join the AWDC finish it and have some fun!!!! Feck you could race it in comp safari if you got it back up tp scratch and the cage is all good.