Firstly, sorry to hear about your work situation. Fingers crossed you'll be ok.
To answer your question, I've no idea about the length of the waiting list (both in terms of numbers of people on the list or the % of those on the list who would take one should they be offered one).
As fair as I understand it, all you have to pay right now is the 20% non-refundable deposit to secure your ST for next season. You'll likely have this amount in credit (and some) due to the games we weren't allowed to attend last season. So no expenditure there. Then, when the stadium opens up with reduced capacity, STHs will be asked to enter into a ballot for any games they wish to attend. If you find yourself in a difficult situation financially, you can simply choose not to enter the ballot. Again, no expenditure. This is likely to be the case until the stadium opens up at full capacity which is anyone's guess when this might be but it doesn't look like it's going to be any time soon. Once the stadium does open at full capacity, your commitment to being a STH will be re-activated and presumably you'll have to pay up front for whatever games are remaining on a pro-rata basis. When the stadium has returned to full capacity, I assume normal service is resumed and the ticket exchange will open as normal.
So you could find yourself in a position where your ST costs you nothing this season and you retain it for the 2021/2022 season where hopefully the financial situation of everyone will be a bit more stable.
I see this season coming as effectively a free pass. If you can forgo the 20% deposit, you could retain your ST for nothing. The only gamble is when stadiums will open at full capacity. Personally, I think it will be Q1 of 2021 at the earliest before this happens so you may have to shell out for however many home games we have between then and the end of the season next year, when hopefully you'll be in a stable position financially and able to afford it.