That is bad.

You had installed backupmenu which is highly recommended if usb-port is broken. But if anything goes wrong and booting into backupmenu fails, there is no way back unless you have something to boot from SD (u-boot can do it f.e.).

Now you can ...

... repair the broken usb-port to get the abilty to flash a fresh fremantle with flasher and "U"-key pressed at boot.

or

... sell it on ebay for half of the price of an used N900 (to some technician that looks for broken devices like this and repairs usb) and pay the double to get one with working usb-port.