If you can get to the bootloader screen you should be able to bring up fastboot and get TWRP back on tablet(or just boot to TWRP temporarily)
Here is the general flow for restoring things, should have everythin you need if you can get fastboot ...
Those zips aren't flashable. You have to extract and restore them.
Do a back up of just the boot partition in TWRP. Just check "boot" and nothing else. Make sure you are backing up to external storage(MicroSD card)
Install 2.4.6 ROM and bootlo...