All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
It is more appropriate in this regard to apply the Sunnah in bidding farewell to a traveler as this is a means of protecting him/her from evil. Ibn ‘Umar narrated that when the Prophet was to bid farewell to a man, he would hold his hand and he would not leave it until the man himself dropped the Prophet’s hand, and he would say to him: “Astawdi’u Allaaha deenaka, wa amaanatika, wa khawaateema A’malika.” ‘I place your religion, your faithfulness and the ends of your deeds in the trust of Allaah.’ [Ahmad, At-Tirmithi, An-Nasaa’ee and Ibn Maajah]
Also, in another Hadeeth narrated by Ibn ‘Umar as well, the Prophet said: “When Allaah is entrusted with something, He would preserve it.” [Ahmad]
As regards what is mentioned in the question, it appears - Allaah Knows best – that it is permissible to do it without believing that it is a Sunnah to do it.
Allaah Knows best.