Customers do not receive notification emails regarding their membership hold when it starts, nor when it ends.
If they are not aware of their membership hold end date, and they have not been informed by the business, they will see this when they are charged for their membership on their next billing date, or when they log into their account and see that the membership has become "Active" again.
You can see which customers currently have memberships on hold by going to Memberships ➜ Membership Tools ➜ Edit/End Holds (here)
If you'd like to inform customers of their membership hold ending, you would need to email customers directly, but we also have a guide outlining how you can end membership holds in bulk and where you'd be able to copy their email addresses here: How to edit or end holds in bulk