My wee 3.3hp two stroke is no bigger in physical size that a 2hp. It has no problem pushing my fully loaded 4.3m sib along at 5 or 6 knots. As long as your 2hp can keep the nose of your SIB into the waves in a rough chop.. you have a chance of surviving...in event of a breakdown on the main.
People often think the Aux is to get home..but IMO its purpose is to give you a fighting chance to get to the nearest
safe land spot.. or to stop the boat broaching in a rough sea.
Better being up the creek with a small paddle than no paddle.