Without manufacturer support they be very difficult to operate (even within the confine of the Russian federation & satellite countries). Wonder if there is any “kill switch” embedded…
In general terms, how often do the manufacturers release software updates for the flight systems ? Even if the possibility of 'kill switches' is a reality, surely the onward march of AD's etc would make the aircraft non-compliant. The Russians can nationalise the leased aircraft but soon enough there will be operational issues that can't be resolved easily, and then of course there will be liens galore.