Of course Sullinger is expendable in any deal for Love, despite Love's weaknesses. However, I don't think this is the right trade for the Celtics now. The team does not have enough talent to surround Rondo and Love with the help they would need and Love would just leave next year like he plans to leave Minnesota. The Celtics need more assets before they make a win now move.
When the Celtics made the trades for Allen and Garnett, they still had Rondo, Pierce, and Perkins left over to round out the starting 5. A deal for Love would leave them with... Jeff Green? Their two biggest needs right now are a defensive big man and a dynamic, scoring GF type (like a Pierce or a George). Dealing for Love would still require those two gaping holes to be filled.