ask tui to honour all deposits till its safe to travel

i and many others are about to lose there holiday deposit ,because of covid 19 the balance of my holiday is due 24/04/20 as youcan imagine at this moment in time i am not willing to give tui over £3500 because if the holiday is canceled tui will only refund a travel voucher but if i want a cash refund i will have to wait a year from my date of travel .how can this be fair