How is it possible to come back from Rome once ended the bike travel along the Via Francigena?
There are four possibilities:
1. High speed or long distance trains, with the obligation to dismantle the bicycle, put it inside of a transportation bag with maximum dimensions permitted by the guidelines (for example for what it may concern Trenitalia: 80 x 110 x 40 cm) and charghe it into the luggage compartment, praying that the opening is big enough and that the train is not too crowded; otherwise it might happen unpleasant discussions with the ticket inspector or with the others travellers. You can find more informations on the Trenitalia website.
2. If you do not want to dismantle your bike. you can use the regional trains with the apposite compartment dedicated to bicycle transportation, paying the specific additional cost. If it is a long distance travel you will be forced to change several times the train, for example from Rome to Milan it is necessary to change train in Florence, Prato and Bologna.
3. You can travel with a long distance autobus, such as Flixbus, integrating the ticket with the option "bulky baggage" and properly packing the bicycle (for example with the bubble wrap and adhesive tape) or inserting it into a bag.
4. The last option is the plane. Usually all the Airlines allow the bicycle transportation, adequately packed. For more details check the website of every specific Airline.