Physically PWInsider has reported multiple times that they were afraid Taker wouldn't be able to go this year, they were discussing doing a Taker-McMahon match since it wouldn't require anything but taker beating him down. If his shoulder doesn't improve, don't be suprised to see a Vince-Taker feud next year, it'd be quite interesting in a Victor Frankenstein-The Monster sort of way, with Vince saying I created you and you'll never reach the 20-0, i'm going to destroy end you at 19-1. Once taker hits 20-0 he'll probably retire, so a the creation vs the creator feud would probably be their best bet, or Cena-Undertaker but if they have Cena lose and then Taker retires it doesn't look that good on Cena.
Either way, on the HHH beating Taker, honestly who else deserves it? As you said HHH will be around forever, he'll be working in the WWE for the next 30+ years, it would be a travesty if they let someone get the ultimate rub of beating Taker and then they left the WWE, they planned on having Brock beat Taker, imagine if they did that? They either have to never have Taker lose, or have him lose to HHH/Cena, they are the only two people that should have enough trust built up that they wouldn't screw it over.