You haven't explicitly said what your circumstances are but if you leave VM, then any email accounts should be closed down 90 days after leaving. If you don't access your email account for 150 days it may be closed down without warning (90 days may lead to suspension and a further 60 days may lead to deletion).
A general shutdown of VM (and prior companies') emails has long been speculated on. VM on here has routinely stated in the past there are no such plans for a general closure of email accounts.
However, VM does not allow new customers to create email accounts and existing customers cannot add new accounts so you can draw your own conclusions on what might happen in the future.
If for no other reason than VM's email service is so very poor and unreliable, you might want to consider starting a process of migrating your email to one of the other free providers anyway. As/when/if VM ever did announce a general email close down, you would be well on the way to migrating your accounts elsewhere. A new email provider would also very likely offer you better security and features than what you have with VM email.
