Presuming the OP is still using the version of Pilot App that was in use at the time of the 1.2.0.17 fw and does not auto-update the app then it is feasible he can stick to this firmware for as long as he wants.
Also, assuming he can still get his hands on batteries (or other updatable components) that don't already have a newer fw version, he can still use the older bin files to bring them in line with his current setup.
If he upgrades his Pilot App to the DJI Go app then he'll be forced to upgrade to the latest fw and will be given the option to regress to 1.2.1.06
Sultan, whilst I agree it is unlikely you'll have need for it, I have Opened a Dropbox account just for you and the files can be found here:
https://www.dropbox.com/sh/hsqrgc2qsv5nf2s/AACGuEomvIk5Dhm1o9FkdjLja?dl=0