I did not watch the video, just read the article, but there is no mention of the unions.

It is understandable that M. leMaire is not happy, as he may soon see the fourth political power in France (the street mob) ask the government to save Alstom. However, I have some doubts that this government will force SNCF to buy another bunch of not really needed TGVs. Instead it could be that they would let Alstom go under as it exists now (this is speculation, of course).

A little bit less understandable is M. Pépy's reaction, as his enterprise (the SNCF) would have to pay higher prices for rolling stock and signalling equipment after the merger. (But then, he also opposed (and had the government oppose) the purchase of Velaros by Eurostar, back then.)