The bootloader is not lost (AFAIK it is in ROM); most probably this is the typical case of infamous "bootvector loss".
During bulkerase, both the data flash and the bootvector gets erased, but that process takes some time. Normally, after bulkerase, the internal bootloader restores the default bootvector (and status byte) automatically after the bulkerase finished. But, if during the bulkerase is in progress, the watchdog kicks in, or any other reset occurs (e.g. poweroff), there is nothing which can restore the bootvector (it remains in erased state, which is 00).
The easiest and safest way to "revive" the chips is to get access to parallel programmer capable of programming these chips (you can try some local programmer vendors, they sometimes provide chip programming as a service, or you can simply try to "talk them" into reprogramming a few of your chips).
With some hints from the 8052.com forum I have experimented with a "bootvector restorer" run from external program memory and I succeeded. However, I had only a P89C51RD2Hxx chip (mind the H in the suffix), which is an older revision than the H-less. So, if you are interested and wish to experiment, drop me an email, I'll send you the details.
Jan Waclawek