Last year to get out of Conques, it was a school day I was leaving on, and I was able to catch the school bus earlyish to get to Rodez. From there I took a bus to Montauban- the bus station was right next door to the train station where they sold me the ticket, and the bus left a couple of hours before the next train. Then I was dropped off at the train station in Montauban from where I took a train in the direction of Toulouse (though I got off at Moissac.)
The other option that the Tourist Office suggested was to get a taxi to the St Christophe station, which is passed through by the Paris train- not sure about where that train goes through to in the opposite direction. The taxi wasn't all that expensive to St Christophe.
It won't be all that straightforward getting out of Conques, and it will take several changes of bus/train- but it is possible.
Margaret