Most of the train ended up in the field or canal. How on earth can it take 7 months to repair a bridge parapet?
It completely demolished / destroyed a significant chunk of bridge structure on the eastern abutment, basically a sizeable reinforced concrete parapet which looks like it was part of the abutment structure. Given the high energy involved, that may well have fractured more critical parts of the abutment.
From the look of things, the steel parapet of the main span is also a main longitudinal support beam. The northern steel parapet had 80100 tonnes (I'm just guessing the weight here, rather than looking it up) of power car hitting it at approximately 240 kph (150 mph), with some major components of the power car (the rear bogie, in particular) basically being stopped dead by the end of the parapet, and others running along the top and inner side of it. I'm not certain, but it seems quite possible to me that there could have been significant structural damage to the main span/deck from this. It is quite safe to say the the entire bridge was subjected to significant forces, loads, and shock in ways that are well beyond its design. It was enough to more or less dismantle much of the power car behind the cab into component parts, and I assume that TGV power cars are reasonably robust, so it takes significant forces (provided by the bridge) to achieve that.
There was also a significant fire involving the bridge, fuelled by the transformer oil (this is a significant quantity of oil, if you are not familiar with large transformers, used to cool the transformer).
I've been unable to find the specifics of the repair effort, so much of this is speculation. I just would not be surprised if the entire deck needed replacement (or at least significant remedial work), and the abutment possibly needed major rebuilding effort. 7 months doesn't seem terribly surprising when looking at it in those terms.