their G36 hasn't been that big of a success their 416 and 417 rifles have done very well. Those rifles are being used all over the world currently. The G36 is still being produced and sold as well. I'm not sure which countries use them but there are more than a few.
Their handguns still do very well. Their sales of their VP series pistols has been pretty good. I think that is in large part because of the VP series price. HK seems to be really trying to compete in a very saturated striker fired hand gun market. That being said I have always been partial to their DA/SA guns. The My favorite is the P30, it is a tank, and an excellent pistol. Over on PT they did a tourture test on the P30. The initial test was supposed to be a 50K round test. They ended up doing a little over 90,000 rounds. Impressed the hell out of me. That is why I own one.
I don't see HK going anywhere anytime soon. In my opinion that is a good thing. While the market is saturated, competition breeds innovation. Ultimately we are the real winners in the great handgun war.