You can revive it flawlessly with Guo's mtk_uartboot!
Download UART boot compatible BL2: bl2-7622-1ddr-ram.bin from the Belkin RT3200 / Linksys E8450 thread:
Build a FIP packaged U-Boot from my branch and feed your device through TFTP after booted it with mtk_uartboot!
$ ./mtk_uartboot --brom-load-baudrate 115200 -s /dev/ttyUSB0 -p bl2-mt7622-1ddr-ram.bin --aarch64 -f openwrt-mediatek-mt7622-xiaomi_redmi-router-ax6s-bl31-uboot.fip && minicom -D /dev/ttyUSB0
It will boot and would ask for files on TFTP! Download them from downloads.openwrt.org!
After it booted OpenWrt, then examine how your NAND is killed by hexdump -C-ing all the mtd devices (/dev/mtd*).
To rewrite your missing partitions just use insmod mtd-rw i_want_a_brick=1 to unlock your mtds!
After unlock a simple mtd write ... will suffice.