I kind of suspect - though I have no knowledge of this having been done - that if you send the remains of your destroyed GPSR back to Garmin, they will allow you to transfer the unlock code to a new GPSR. The reason I suspect this is that Garmin is a fairly customer-oriented company, and also, because it's really Navteq who are the ones that impose the 'licence code locked to GPSR serial number' protection system on what is Navteq's intellectual property. It certainly would be in Garmin's best interest to facilitate a serial number transfer - because that way, they sell another piece of hardware, and Garmin is primarily a hardware company, not a software (map) company.
My suggestion - and keep in mind this is just a shot in the dark - is that you write Garmin a nice letter, explaining what happened and that you intend to purchase a replacement GPSR, and asking them if they would be willing to transfer the licence for your existing cartography to your new unit if you send Garmin back the damaged GPSR.
Worth a try, only costs a stamp. Don't try to complicate matters by asking for your dead GPSR back, etc. - just keep it simple, you send them the dead GPSR, they send you a new (replacement) unlock code for your new GPSR. Plain and simple.
PanEuropean