Like Irving has said a failure like that could have caused all sorts of other damage, if your still thinking about a complete change out then why not sit down & work out the cost & put that to the owner as an option, you will need a BOB, 3 x drivers, power supply, software licence for mach3 that you already know of then a small safety type circuit, got the layout for mine from on the forum & didn't cost much to build, few relays an estop & some wiring basically. You could use the machines existing estop for this so that helps reduce the bill, I built my control box before I got the gerber for something else I had started before it came up & it was all built into an old computer case.
Original motors are superior electrics slo syn can't remember model but they are 1.8v, 4.7A 6 wire nema 34. If you intend to use the original mators then you need a 36v power supply & drivers to match. I will eventually fit nema 23 motors that will handle a higher voltage so the drivers I have fitted are wasted just now as they are capable of a lot more but until I can make some adapter plates for the motors I'm limited to 36v.
If your looking for info on step & direction then I would need to double check this & my notebook is at the unit but I think it goes
Green A
Blue A-
red B
Org B-

Black & white are centre taps, black for red, red/white & white for green, green/white

Like I say don't take that as written & go applying any external power but should be ok for testing.
will update that latter after I have been up at the unit. Might not be the best idea to buy the cheapest drivers you can find, remember this will be a production machine for a business if plans go well & could be doing a lot of hours running.