Tried to replace the belt tensionser and where it connects to the engine snapped right off, can it be welded, fixed without replacing entire engine?

There is a single bolt that fastens the tensioner to the block. The tensioner itself is a spring loaded mount and pulley and can be removed from the engine block by the single center bolt (I believe it is a 10mm bolt). The tensioner also has a tab that prevent it from spinning that fits into a hole on the block. Did you snap the 10mm bolt off in the block? Or did the pulley on the tensioner come apart? If you can get the bolt out, just chuck the tensioner and replace it, if the bolt snapped off, you'll have to have it extracted, and possibly retap the hole. Any competent shop should be able to get a snapped bolt out, you can also pick up bolt extractors at any parts or tool store.