I wouldn’t expect the tree to die after pruning unless the work was careless or excessive. Depending on which branches are cut and the extent of the work, pruning can be stressful for the tree and slow down development. I usually take the conservative route and start with the roots before doing a lot of work on the branches. Considering how healthy the tree is, I think you’d be fine styling it now and looking to repot next spring.
I always deal with the roots first when obtaining new stock either from a nursery or otherwise. The key factor for me is to be aware of root condition and thus the ability of the plant to handle developmental work. In particular I like to establish the basic rootball needed for Bonsai development and long term health before styling.
This ensures that any hidden issues in the soil are addressed and one can gauge the length of time needed for recovery before styling or heavy pruning usually required to compact the tree and increase interior foliage.
I would vote for repot in the spring first.
So I did style the juniper and pruned branches off the roots were in good condition and some branches had roots so I cut those off, I think itl be a learning experience for me nit to touch roots before styling If tree declines, I won’t touch or prune next year , maybe reduce roots to a training pot.
I’ll pray it survives
I expect it will survive - what’ll be interesting is to see if any areas fill in stronger than others. If the tree grows evenly, you’ll have done a good job!
Seeing how the tree responds will also give you time to figure out the next steps for working out the future style and where to go from here.