While the following is not probable, due to the obsolete hardware, should a competent individual choose to pursue this:
I utilize OpenWRT for my WRT1900ac and one of the OpenWRT devs was able to work with one of the makers of U-Boot to repair a corrupted bootloader on the WRT1900ac. This would seem to offer at least a minute, albeit slim, chance one could reach out to whomever [individual or company] wrote the bootloader for this device in order to garnish the required files and commands to rebuild the bootloader.
For an example on how simple the process is once the files and commands have been garnished, please take a look at
for the WRT1900ac
One of the hurdles one would also have to overcome is discovering if commands can be pushed via the device's USB port, or whether there is a serial port on the device's board itself, as the commands for the WRT1900ac must be given via the serial port.