If one is in doubt if he made Kiddush Fri night, or if it was made correctly, he cannot repeat it (although it is good to hear it from someone else).
In the event that he cannot hear from someone else, he is allowed to eat normally, although it is forbidden to eat before Kiddush.
Would it be an act of piety to eat the bare minimum that one is required to eat on Shabbos, in such a case, as every bit of food that one enters into his mouth is possibly a transgression of eating before Kiddush? (Obviously, this is talking about a person who is on a high madreiga…)
In a case that a person is an “ones”, and cannot make Kiddush, then the halacha of Kiddush b’makom seuda will not apply. Therefore he may eat regularly, and it isn’t as if he is doing a transgression with every bite, and he should rather eat regular and fulfill the mitzvah of oneg shabbos.
Pri Megadim Pesicha Koleles 3-8.