In response:
* We know we have had it good for 7 years, we just thought that Bob would keep going for ever

* The garage we are dealing with is a Bongo savvy garage (they are listed on here) but they have said they don't fit any part that is not got direct from Mazda so there's no chance they would fit us a second hand ABS pump - but we can't believe how cheap 2nd hand ones are! This may well be a good option for us to pursue.
* the van is not converted (we had intentions to do that but it's so useful as is to carry kids and kids' crap around!)
* the MOT is due February and the body work is decent (although this is off the top of my head, I would have to investigate further when we get the van back)
* AND, the brakes do work without the ABS pump working. I have assumed the ABS pump is an extra level of 'brake security' as the van can still be driven without it working.
We are still deciding what to do - and now the option of getting another van has presented itself, we may just take the opportunity to get a freetop and perhaps a converted one.
Anyway, thank you so much for the comments, we are very grateful.
Carl and Lucy