My TB has just had over 8 weeks off due to having a virus and me being on holiday for 2 weeks. I hopped on him the other day and took him for a 45 minute hack, walking only. He was absolutely fine, nice and forward going but not silly. He had been living out during the whole period though which I think makes a difference. I'm sure things will become more exciting though when we step it up a gear
I think it really depends on the individual horse and the reasons it has been off work, all horses will react differently to the time off!