Good question.
Ukraine shut the canal down in 2014 when the Russians invaded Crimea. The Russians managed to get it flowing again last March, after they invaded Ukraine.
So they they got along without it as a water supply for eight years.
I have no idea how well they got along without it.
From the reports I remember, not too great. They've significantly depleted the Crimea aquifers, had to truck in a lot of water across the Kerch Bridge and the area under cultivation has been reduced (though Russia claims that output is up).
According to official Russian statistics, the Crimean agricultural industry fully overcame the consequences of the blocking of the North Crimean Canal and crop yields grew by a factor of 1.5 from 2013 by 2016
These official statistics contrast with reports of a massive shrinkage in the area under cultivation in Crimea, from 130,000 hectares in 2013 to just 14,000 in 2017, and an empty canal and a nearly dry reservoir resulting in widespread water shortages, with water only being available for three to five hours a day in 2021
https://en.wikipedia.org/wiki/North_Crimean_Canal