We have wild muscadine all over our woods. Problem is they are huge and are high in the tree tops so we can't reach the grapes. Can these be cut of at the base of the vine and trained to grow back on a lower trellis or would they just die off? Most of the vines are about 2 to 3" in diameter at the base.
You can just cut the trunk down during winter dormancy and it will sprout back.
Then train to your desired shape as if new.
Muscadines are only harder to root than other grape species. They are still vigorous weeds. The cut can be a vector for wood disease, but it is unlikely you will kill them.
The only thing I would consider is light as there is a reason they grew up to the treetops in the first place.