Dev could have lost it altogether and joined the Axis. Imagine the big stupid head on him next to Il Duce and the Fuhrer. The Brits would have absolutely flipped and probably would have occupied us again. We would have been seen as total scum to the rest of the English speaking world.
There was no likelihood of Dev aligning with the Axis.
Despite pleas from the UK, and earlier France, the US remained resolutely neutral even after Pearl Harbour. It only entered the war in Europe after Hitler declared war on it. Hitler never declared war on Ireland in the same way.
It is also not likely that there would have been any popular support for entering the war amongst the general population here.