Amtrak general refund policy--including for no-fee fully refundable tickets such as Acela First Class--is that refunds are always to the original form of payment. If this is the policy applicable to a refund for an Amtrak-canceled train, then your refund would be in the form of a new eVoucher if you paid for the ticket on the canceled train with an eVoucher. Whether an Amtrak agent would be willing to waive this general rule and give you a cash or credit card refund on a ticket paid for with an eVoucher is an open question, but I would not be particularly optimistic.