Can a nearly all-white leaf keep going with just a few green spots?

I’d leave it for now. The green spots may do a little photosynthesis, but the plant’s other green leaves are doing most of the work. One very pale leaf by itself isn’t a reason to cut it off.

Watch what the next growth does. If it keeps coming in all white, consider pruning back to a node where the stem shows green. That gives the next growth point a better chance of producing some green, though it isn’t a guarantee.

There isn’t a reliable number of green spots that tells you whether the leaf can support itself. White tissue contributes little to photosynthesis, but the plant’s overall condition depends on all its leaves, not this one alone. If the rest of the plant is growing normally, waiting is reasonable.

Keep its usual care steady and give it bright, indirect light. More light won’t turn white tissue green, and a sudden jump into strong direct sun can damage leaves. Check the stem near the growing point too: green there is encouraging, but it doesn’t promise the next leaf will be greener.