If you used the initramfs to save a copy of the firmware partition before flashing OpenWrt, then you can just flash that file back by using it as a sysupgrade (with -F to force install and -n to not try to save settings) in OpenWrt. The router will reboot to RouterOS exactly as you left it.
I don't have any experience with reverting mikrotik boards from openwrt.
But I was succeed to use netinstall mikrotik utility a few times to recover some unresponsive units.
You should give a try with this option.
fixed ip on you computer: 192.168.1.2
disable firewall and any antivirus program.
count 10/15 sec before release reset button,
And don't expect to get netinstall discover your unit at 1st try. Some time at 1st try it works, some time you will take 10 attempts.
I suggest you try a few different / older Netinstall versions, that's how I was able to restore RouterOS on my RB750Gr3. Neither latest v7 nor latest v6 Netinstall worked for me, however I used 6.44.5 which DID work.
You will know it works when you see the progress bar while formatting the flash as well as installing the OS - make sure you get the matching Netinstall and RouterOS package versions
Same here, I used netinstall 6.47.9 and 6.48.6 to recover some rb711g-5hnd and RB450G.
But no needs to use a matching Netinstall and RouterOS. With these 2 ver, I was able to recover a few mk units to OS 7.1.2
While running OpenWrt you can configure boot options by writing to the files in /sys/firmware/mikrotik/soft_config. In particular the Mikrotik tools probably need boot_proto to be bootp. Write a 1 to the file named commit to write the change to flash, then cut the power and reboot. Holding the button until the LED goes out should always force a netboot.
this is new thing, can you elaborate more about " Write a 1 to the file named commit to write the change to flash", sorry not really a tech guy LOL. did you mean i should change the default content of boot_proto from "dhcp" to "bootp" and save it, then just turn off the router and try again with netinstall ?
Reading "clean" from commit confirms the changes have been saved to flash. Then you can reboot holding down the reset button and it should execute a BOOTP netboot.
Also you can look at the settings in boot_device but you probably want to leave flash as an option so you can get back to OpenWrt if RouterOS doesn't install.