Triple H has been around the WWE for quite a long time. He's one of the industries' top performers, he's been at main event status for a while, and he is great at giving promos. To be honest, claiming if he'll be missed can go multiple ways. There's honestly no straight cut answer, because there's so many factors that can find its way into it.
The business will definitely miss his in-ring performances, just like they'll miss Shawn Michaels; but they'll replace him. Yes, he's one of their top men - but the thing is, unlike Shawn, Triple H is here to stay. With him being included into the McMahon family, he's bound to take up the business with Stephanie behind the scenes. So even if he ends up leaving our TV screens from actual wrestling, he's most likely going to end up being televised anyway because of those relationships (whether they make him a General Manager, or just behaving in a similar manner that Vince does now).
As for the fans, it's difficult. For some of us who have known him since WWF, I'd say that people would miss him, even if it's just out of nostalgia. Some, of course, are bound to say they wouldn't; but we know that if sometime down the line he was brought up in conversation, we'd remember him instantly. The impact he's made on the fans, whether you love him or hate him, is what will keep his legacy going. So in truth, I think he would be missed (he's a damn good heel, that ass).
But those of us who have only been introduced to him in his PG state of behavior might not be able to make the same statement. In fact, most of the characters I've been introduced to during the PG era slip my mind pretty quickly. It's hard to give people character when you're putting limits on what they can do behavior-wise. Triple H has become nothing short of a comedian (and a cheesy one, too) off the stage from what I've seen, and because of his injuries and age, he's naturally slowing down in the ring. He's not shot, but I just can't see how he'd make a huge impact on the crowd today as he did back then.
But, I'm open to being wrong, as I haven't really paid attention to wrestling for a long time after the Attitude Era faded.
TL;DR
Triple H will naturally be missed by the company and age-old fans, but that's how it is for everyone who's been there for a long time. Now you just have to wonder when he actually will decide to hang up the boots.