I have not been following MP for a while now, however over the long run, the bankroll profit of a casino will be roughly the HE times the amount wadgered at the casino. The fact that the owners of the casino are different then the owners of the bankroll means that you will need to trust that the owners of the casino are not cheating the owners of the bankroll (I have no reason to believe this is the case).

The fact that MP takes a portion of the HE regardless of if the bankroll is profitable or not somewhat complicates things, however the above statement should generally be true.

To the extent that (a) you will not need your investment in the medium term, (b) trust that the owners of MP are not cheating the owners of the bankroll and (c) believe that MP will continue to have similar or greater betting volumes then you should keep your investment. If any of the above is not true then you might want to divest.