I'm not sure if I understand your question regarding exposure. That's for you to decide. I think Travel Bank and TrueBlue points are equally worthless. It's up to you to use the Travel Bank before it expires. Points do not convert to Travel Bank, and Travel Bank does not convert to points.

All refunds are processed into Travel Banks (and points redeposited into your account) unless you cancel within 24 hours of booking, in which case it goes to the original form of payment per the DOT rules.

A sale does not make a difference. A published fare is a published fare and the applicable fare rules apply. Unless you use a special code with its own T&Cs then it is a published fare -- a standard Tuesday sale such as the recent 20% off TB sale is a published fare. If you cancel and rebook (or change your flights) down the road you will be responsible for the fare difference up to the currently published fare. If you cancel and it was 20% off and you spent 5k points (normally 6,250 points) and $5.60, you will get 5k points back and $5.60 in Travel Bank. It does not matter if there is a sale -- a published fare is a published fare.

-J.