as long as the bolts still holiding the top and the balljoint aint got to much movement as if the balljoint or the bolt give in (maybe over another pothole) then the driveshaft still drives the wheel but its not held to the wishbone making the wheel drive into the bumper and up into the wing,
jack up and see how much movements in the balljoint you 'should' be ok aslong as its not just got a hold of the wheel,
my mot car needed balljoint and cj joint but it went to testing station with spare shaft in the boot and i was 9.60 for a ball joint from local motor parts thats a mk2 ph1 1.6,
jack car
remove wheel
take out bolt going from hub to balljoint-2 sockets as the head will spin(watch the bolt doesnt snap this happend to me when replacing diff circlip and cost me an extra hour trying to find a balljoint bolt).
with top bolt out big lever wishbone/anti-roll downwards till balljoint pops out then release lever slowly making sure not to pop cv joint or cause damage(maybe better to get a friend lever so you have 2 hands for hub and balljoint).
two bolts from ball joint to wishbone- need spanner maybe even a ring spanner not a open one at the top bolt heads and socket underneath,allow spanner to use the wishbone to counteract the loosening pressure from socket underside and also as driveshaft makes it hard to hold bolts from above.
with two wishbone bolts off balljoint is ready to be replaced,
same as removal wishbone bolts bk on first then lever down and pop in balljoint before puting balljoint to hub bolt back threw(unsure if theres threads inside the hub an balljoint or if its just the bolt but i make sure the bolt faces the same way-head to front bumper and nut to floorwell/rear