V.W.
Are you worried it isn't healing properly? Or is it more of you are worrying he'll have to "re-learn" how to walk?
It hasn't even been 10 days yet. I would give him a little more time. There's no rush. I doubt you'll have to "work with him" to get him back walking, once the fracture is healed. He might still have a little discomfort that he just would rather not feel...and not standing/walking on it too much lets him not feel that. As soon as he doesn't have any pain from using it, I'm sure he'll be right back at things.
If he still isn't doing any walking when you go back on the 16th, ask the doctor about it. And go ahead and ask him then anyway, about ANY questions you have. Write them down before you go, so you don't forget... forgetting your questions is easy to do when you have kiddos with you and the doctor is in a rush... Jot them down as you think of them (like now) and keep the list in your purse. Pull it out when you get to the doctor's office/treatment room.
I bruised my knee when I fell ice-skating just before Christmas. I avoided walking or doing anything weight bearing (that I COULD avoid) for several days. And when I did try to do more, I was a little cautious. And sometimes doing a little more, made it a little more sore for the next 6-8 hours or so... so I stayed off it in stretches. Your son is no different. He will try what he is willing to tolerate (aches/pains wise) and then stop when he feels something uncomfortable. And standing some may increase his discomfort over the following hours for a bit. I wouldn't rush it.
And next time make sure they remove the shoes on the slide. ;)