You mean Prime Minister right, Erdogan may proceed to be the next President. I can't imagine anyone else taking over that mantle (unless people with criminal record can't become Presidents, Erdogan was jailed once).
Remember the President is only a symbolic position, however any disharmony between the President and PM effects the political stability, so it has to be someone from the same cast as the government.
(I remember when Necdet Sezer threw the constitution after Bülent Ecevit in a fit of anger, and that was a disaster for the political stability of Turkey!)
Actually the President is not symbolic in Turkey.
Here is the list of his duties and responsibilities:
to deliver, if he deems it necessary, the opening address of the parliament on the first day of the legislative year,
to summon the parliament to meet, when necessary,
to promulgate laws,
to return laws to the parliament to be reconsidered,
to submit to referendum, if he deems it necessary, legislation regarding amendment of the constitution,
to appeal to the Constitutional Court for the annulment of certain provisions or the entirety of laws, decrees having the force of law, and the Rules of Procedure of the parliament on the grounds that they are unconstitutional in form or in content,
to call new elections for the parliament
to appoint and to accept the resignation of the prime minister,
to appoint and dismiss ministers upon the proposal of the prime minister,
to preside over the council of ministers or to call the council of ministers to meet under his chairmanship whenever he deems it necessary,
to accredit representatives of the Turkish State to foreign states, and to receive the representatives of foreign states appointed to the Republic of Turkey,
to ratify and promulgate international treaties,
to represent the Supreme Military Command of the Turkish Armed Forces on behalf of the Turkish Grand National Assembly,
to decide on the mobilization of the Turkish Armed Forces,
to appoint the Chief of the General Staff,
to call the National Security Council to meet,
to preside over the National Security Council,
to proclaim martial law or state of emergency, and to issue decrees having the force of law, upon a decision of the council of ministers meeting under his chairmanship,
to sign decrees,
to grant full or partial clemency, on grounds of chronic illness, disability, or old age, all or part of the sentences imposed on certain individuals
to appoint the members and the chairman of the State Supervisory Council,
to instruct the State Supervisory Council to carry out inquiries, investigations and inspections,
to appoint the members of the Higher Education Council,
to appoint rectors of universities.
Yes the list is quite long
Edit: But i agree that Erdogan should leave the stage and more professional people should get a hold of the AKP. Egemen Bagis is the best candidate in my opinion.
But no matter what, Erdogan is in my view the biggest Turkish personality in our history,