Honestly, it's something we all are watching to some level of degree.
Luckily, we didn't put all our eggs in the Heath basket, bringing in a journey man level guy in Blanton, drafting Woods and Fraizer was drafted last year.
So, if Heath can't handle it, we can rotate again to play to each players strength in the mean time.
Personally, I think he will fine back there. His rookie year he didn't make any terrible mistakes. He knew where to be, just that the NFL gameplay/talent was a huge jump in playing level for him IMO. Having a D-II player step in right away and play against the top players in the game won't give you favorable results.
His limited snaps after his rookie year has shown that he is in the right place at the right time and/or knows where to be. He has capitalized on those situations too. His play in the Green Bay game was also encouraging as well.
I think the FO/staff saw something in him last offseason to give him that 4 year deal. At worst, it becomes a good salary for a good STer. At best we get a guy who can play meaningful snaps on defense for peanuts.