How should an AVL tree be rotated if it is both a right-right case and right-left case?

The AVL tree in the following figure is generated by removing a leaf node in subtree T0.

After the node has been deleted, the tree becomes unbalanced.

Should I regard the below condition as a Right-Right case or a Right-Left case?

It is a Right-Right case, because node 𝑦's balance factor is not negative (it is zero).

Wikipedia's section on AVL rebalancing lists these possibilities, but realise that the nodes are labelled differently:

Let X be the node that has a (temporary) balance factor of −2 or +2. Its left or right subtree was modified. Let Z be the higher child [...]

• Right Right ⟹ Z is a right child of its parent X and BF(Z) ≥ 0
• [...]
• Right Left ⟹ Z is a right child of its parent X and BF(Z) < 0

Using that labelling for your tree, you would picture it like this:

        ____44____             BF(X): 2
       /    X     \
     17          __62__        BF(Z): 0
    /  \        /  Z   \
   10  21   __50_       78
           /     \     /  \
         48      54   72  88
        /  \    /  \     /  \
       45  49  52  56   81  92

So we are in the first (i.e. Right Right) case.

Wikipedia continues with the action to take:

And the rebalancing is performed differently:

• Right Right ⟹ X is rebalanced with a simple rotation rotate_Left

This simple rotation will give this tree:

          ____62____
         /    Z     \
     __44__          78
    /  X   \        /  \
  17      __50_    72   88
 /  \    /     \       /  \
10  21  48      54    81  92
       /  \    /  \
      45  49  52  56