Likely:
1) Not enough time left for the Al to amalgamate.
2) Not enough, or bad, Mercuric Chloride.
3) Wrong type of Al.
Less Likely:
4) Too much / too little water. If there is too little water in SWIM's experience the flask will clog up with Al(somethingorother). It's in the F* Search Engine. Too much water I don't think would make a difference.
5) Some contaminant in your reaction, maybe from improperly cleaned glassware.
If the vast majority of the Al didn't get used up, then the reaction is most likely close to a 100% failure. There may be a few percent of the expected yield still in there.
If you extract the reaction as it is now with Xylene/Toulene or other NP you may end up with a YELLOW tinged solution. This should/may be your MDP2P mixed with whatever other crap formed in the reaction. I've found if the extracts are yellow (the NP extracts I'm talking about) the reaction was usually a dismal failure.
I'm no expert but am quite experienced with this reaction.