Fuel depots and reserves are military targets yes but targeting every single fuel depot of fuel reserve is a war crime because civilians use them too.
Which is where your problem is. Any remaining fuel depot or reserves will be under military control and kept for military purposes. You are assuming that the military will allocate fuel supplies for civilian usage. If the island is blockaded, then the military will requisition all remaining supplies for military operations. The only fuel that civilians will be able to obtain is at the gas station which will be pumped dry by civilians or the military within 24 hours.
If the ROC military runs out of fuel then the ability to quickly move supplies and troops is severely hampered. It will be imperative for the military to stretch the available resources for as long as possible under a blockade. The compliant about potential war crimes is overblown. Civilians will not have access to remaining fuel supplies.