AccuScore simulated how the Rockets would perform against the rest of the teams in the Western Conference who are currently making the Playoffs – one simulation with Yao Ming healthy, the other with him injured.  On average, the Rockets winning percentage dropped nearly 6 percentage points.  The Rockets have 26 games left on the schedule.  If you extrapolate that -6 percentage points across 26 games they win 1.5 fewer games.

Houston Win %	LAL	@LAL	PHO	@PHO	SA	@SA	UT	@UT
W/O Yao Ming	43%	32%	51%	36%	44%	31%	57%	30%
W/ Yao Ming	54%	40%	59%	39%	52%	31%	63%	33%
DIFF (+/-)	-11%	-8%	-8%	-3%	-8%	0%	-6%	-3%

Houston Win %	DAL	@DAL	GS	@GS	NO	@NO	AVERAGE
W/O Yao Ming	46%	31%	69%	51%	45%	37%	40.5%
W/ Yao Ming	53%	33%	82%	60%	53%	43%	46.4%
DIFF (+/-)	-7%	-2%	-13%	-9%	-8%	-6%	-5.9%

Currently, the Rockets have a 2.5 game lead on the 8th Seed, Golden State Warriors and a 3 game lead on the Denver Nuggets (9th in the West). Even with the large 6 percentage average drop the Rockets still have a good chance of clinging to a Playoff Spot.

If they end up with the 8th spot, they seem to be headed to a first-round match-up with the Lakers.  If the Rockets had Yao Ming they had a fighting chance to upset the Lakers (54% winning at home, 40% on road), but without Yao the Rocket win just 43% of simulations at home and 32% on the road.  You can imagine why Houston would struggle with the combo of Pau Gasol and a healthy Andrew Bynum punishing Houston in the post without Yao Ming.