What options are there for getting from Halkali station to the station where the Sofia Istanbul service originally terminated.
For the Sofia Express, best way is using the connected bus service. Train will wait for bus in any case. There are also bus services to Halkali.
Note that, by the end of this year, 2nd phase of Marmaray project will be commissioned and suburban service will reach Halkali, which will be the best way to reach Halkali. Some train services are expected to reach Sirkeci then.