Articles 1 and 3 of the Presidential Permit for KXL are notable. Revokable at any point by the President and, if revoked, the conditions seem to stipulate that everything must be removed with no claim for damages available to the permitee. Cc @EnergyLawProf who might correct me.
Perhaps an #ableg reporter should ask @jkenney about these clauses in the Presidential Permit (he won't likely answer me) since it could possibly end up being AB on the hook for the $ which would be needed to remove the pipeline in addition to the $ already spent to build it.
How? My assumption is KXL is walled-off from TC energy proper and that AB's debt guarantee was to the project structure, not TC proper. The project, if cancelled, would have no revenues, therefore would not be in a position to repay any of the debt which was guaranteed by AB.