It is permissible to say Allah Hafiz as you asked:
Is it okay to say “Allah Hafiz” at the end of conversation?
In truth, concerning using some greeting words (and at the end of the conversations, such as Allah hafiz or Khoda Hafez or …) it should be said that those words would be related to the cultural matters which apparently are not haram in general according to the culture of every country (unless they have bad meanings…).
As far as I searched, apparently, people (Muslims) or at least Arab Muslims used to say Salam (Salamon-Alaikum) before. And I reckon that’s why it is still said A-Salam-o-Alaikum (instead of Hello and even Goodbye). Since it is seen that in some Arab countries people say A-Salam-o-Alaikum as well (instead of Goodbye). Of course they says other phrases such as Fi-Aman-Allah or Ma’a-Salama too.
Even I found a relevance narration that even Imam Hussein (a.s.) used the word SALAM at the end of …
ان الحسین لما نظر الى اثنین و سبعین رجلا من اءهل بیته صرعى ، التفت الى
الخیمه و نادى یا سكینه یا فاطمه ، یا زینب ، یا ام كلثوم ، علیكن منى
Approximate meaning: … Imam Hossein told them my last Salam to you…
Note: It can be better if you (and other Muslim) endeavor to use Islamic phrases in such positions instead of not-Islamic words as much as possible. Although the above-mentioned word "Allah-Hazez" seems to be a nice OK word as well.