That assumes that Bombardier can actually make money on the order. If they are losing money on each streetcar (say perhaps it takes 2-3 times as much labour to assemble as originally anticipated), then there is no resale value.
Quoting JPM's credit guys: "(Bombardier) Transportation Has Value but What’s the Plan?
"The most value ... resides in Transportation, which contributes $5.5 bn based on 2017 EBITDA of ~$675 mn and an ~8x multiple. This represents moderate growth off the ~$600 mn we expect this year. While there may be some opportunity for margin expansion, the ~6% EBIT margins we estimate for Bombardier are not far off what we see in the rest of the sector.
"Strategically, there are a range of options for Transportation. There are no synergies with Aerospace and therefore no reason these two businesses need to reside within the same company. There is an argument that Transportation’s steadier cash flows provide a nice balance to the more cyclical aerospace businesses but it is not clear to us that the business will not be sold in its entirety, particularly if Bombardier needs cash, and control of Transportation would make the asset far more valuable.
...
"Since BA standalone would be a much more cyclical company, to mitigate credit risk, we think it’s reasonable to assume most if not all proceeds from a BT sale would be used for debt pay down. Regarding Bombardier’s role in industry consolidation, we do see this as a logical path, given the threat posed by China Railway as well as the fact that Bombardier has not been able to invest as much in higher value signaling in recent years and is unlikely to in the future due to Aero cash requirements. While it makes the path to consolidation less clear, management’s stated preference to remain in the rail business suggests some kind of JV."
It's possible that the Thunder Bay plant could be targeted for closure in a sale/JV/bankruptcy, but given that BT is throwing off cash and is the most valuable part of the company, one needs to jump through a lot of hoops to get to a scenario where any BBD company reorganization would negatively affect the TTC order. The union issues were much more trouble than a possible bankruptcy, from a slowdown point of view.