I don’t mean to break your train of thought but I have just travelled by Eurostar and every seat was taken, St Pancras was rammed as well. Whilst this is obviously just an anecdote, it matches my other experiences with Eurostar so I don’t think there’s much financial risk for them.
When I have traveled by Eurostar loadings have been pretty healthy (I have traveled 4 or 5 times in the past year or so, once to Paris and the rest to Brussels). However it should be remembered Eurostar are running less trains, and are having to restrict the amount of seats on morning peak trains due to Passenger capacity issues at St Pancras.
According to Companies House, for the 2021 Accounts Eurostar International Limited reported a net loss after tax of £249.2m, for the 2022 Accounts EIL reported a net profit after tax of £65.1m.
Net Profit after Tax in 2019, the last pre-covid year, was £56.4m (although 2018 had been £66.7m).
So it appears that after emerging from Covid restrictions, the profit from the Netherlands section (4 trains per day, mind you), is happily compensating for the profit lost by closing the Kent stations.