Did you try a new cable? WD's My DVR Expanders have a history of poor quality eSATA cables (although the more recent issues seem to be better). The recommended SIIG Serial ATA external cable
is less than $12. Otherwise, and I hesitate to even say it because the odds are that it won't work, but if you're really desparate you could try making an exact copy of your eSATA drive.
TiVo recognizes the WD My DVR Expander by the model number. The only other possibility would be to connect it and your new/replacement eSATA drive to a PC and run dd to make an exact bit-for-bit copy of the drive. It's possible (but not probable) that TiVo might recognize the new drive as the old one and some or all of your recordings could be saved.
Otherwise, pdonoghu's advice is correct, there are no other "thoughts" or options. If your eSATA drive is dead, it's dead and unfortunately all of your recordings since it was connected are history.
Next time it might be best just to upgrade the internal drive and reduce the fail points. More info can be found by clicking on the link below my sig.
Best of luck and let us know how it goes.