The DfT can take the route back, but there are precedents where an incumbent has received an extension due to a delay, something which VT might argue should apply this time. They may also try to obtain an opinion that had the process run properly and the bids measured properly they may have won it (something that DfT have conceded), and they have potentially suffered a loss as a consequence. DfT might also want to consider the wider implications - yes those who might favour renationalisation lite, might see an attraction in all of the other franchises taken back at their end point- but really? Would they want to do that?
In the words of the Act, DOR would be appointed as an 'operator of last resort' when actually they're not, there isn't a threat to services, VT are quite capable of carrying on and are willing to do so.
Taken together, DfT would be well advised to ask VT to continue, not least from a common sense perspective.
When in a hole, the Transport Dept should stop digging