You have to look and see where the Celtics would have finished. They might have been an 8th seed with CP3 the next few years which would mean Big Al never would have been drafted by Danny. Its a compelling thought, but its more difficult than just swap out Pierce for CP3 and keep the team as it was.
Big Al was drafted in 2004. The players Moranis mentioned were all guys who were already on the roster.
We very well could have still ended up with Rondo, too. We ended up picking him with the 21st pick in the draft. With a CP3 / Big Al core, we probably finish outside the lottery, and pick Rondo in the mid- to late teens.
Eventually, Danny would have had the ammunition to pull off a big deal, with some of his expiring contracts, etc. I don't think Ray would be here, and perhaps Danny would have wanted somebody younger than KG. Under those circumstances, I can see the team pulling off a Pau Gasol trade. Hopefully, Rondo wouldn't have to be included.
Regardless, you're looking at a team of Pau/Big Al/CP3 as a core. That team may not win a title, but it's fun to watch.