See here where the answer to your question appears to be "both".
Regarding adding a special request for a safe return trip, a great number of the sidurim that the author has perused have no such
insertion.
In sidurim following Nusach Chabad there is a parenthetical statement
that if one is planning on returning right away he should insert the
words “vesachazireinu leshalom” (ותחזירנו לשלום) — “and return us in
peace.” Thus, he would recite the Tefilas Haderech just once, on the
way there. However, on longer trips, it appears that these two words
are not said .
“Returning immediately” means before the next morning.
However, according to HaRav Betzalel Stern, the words “vesachazireinu
leshalom” should always be inserted when one has intention of
returning home, even if it will be after a long absence, such as a
prolonged business trip, vacation, and the like. If, however, one is
making a one-way, long distance move and is not returning, these two
words are not added.
Of course other nuschaot have ותחזירנו לשלום.
A similar approach can be found here. It says:
Another phrase in tefilas haderech over which there is a disagreement
is, “return us to our homes in
peace.” Some are of the opinion that it is unnecessary to specify this
as it is included in the phrase, “and cause us to reach our desired
destination,” while others include these words in the text. The
prevalent custom is to include this phrase if one intends to return
home that day. (Sefer Ishei Yisrael 50:2, footnote 3)
This "prevalent custom" fits with what I have been taught that the validity of a Tefilas Haderech is only up to the next morning and so there is no need to say ותחזירנו לשלום if you stay longer.
