Mishna Nedarim 2, 2 - 3:
... [but in the case of] oaths, [the action is] permitted, because one cannot [swear an] oath to transgress a mitzvah of the Torah. // There are instances of a [valid] vow within a vow, but there are no [instances where an] oath within an oath [is valid].
Mishna Shevuot 3, 7:
An oath that [I will] not eat this loaf, an oath that [I will] not eat it, an oath that [I will] not eat it, and he ate, he is only liable once
See Gemara Nedarim 16b - 17a:
For it was taught: If one swears to annul a precept, and does not, I might think that he is liable, hence the Bible teaches, [or if a soul swear, pronouncing with his lips] to do evil, or to do good etc. : just as doing good refers to something optional, so doing evil refers [only] to something optional. This excludes one who swears to annul a precept, and did not annul it, because it is not optional! - One verse is to exempt him from the sacrifice due for [violating] an oath, and the other is to exempt him [from punishment for having violated] the injunction concerning an oath.
So we can deduct that if he made a first oath not to bake bread on Tuesday, and afterward to bake a bread on Tuesday. The second oath does exist but has no lav and no Korban because of the first oath. If he cancels the first oath, the duty toward the second oath would be started (the second oath will "find a space" according to the words of Gemara Shevuot 27b). In the case of the OP, I think that the second oath is not relevant regarding Lav and Korban for the case in which people came Tuesday. You are right that somewhat is present but potentially only (it has no "space"). (see Gemara Nedarim 18a, Shevuot 27b and Rambam Haflaa, Shevuot 6, 17 with explanations of Kesef Mishne and Radbaz)
In conclusion, Reuven cannot bake bread. If he can make a "sheela" to the Bet Din, to find a heter, very good, if not, he cannot bake. Someone else need to bake the bread.
Loss of money is not relevant without hatarat shevuot, but for petach and charata this can perhaps count. As a Mishna with Rabbi Akiva (Nedarim 9, 5).