(Mishnah): If one was permitted to leave the Techum (e.g. to testify about the new moon or to save lives) and he found out that the Mitzvah was already done, he has 2000 Amos [from where he was when he found out] in every direction;

If he was still inside the Techum, it is as if he never left.

Anyone who leaves the Techum to save may return to his place.

(Gemara) Question: (Since he was permitted to leave, obviously he has 2000 Amos!) If [our Mishnah] did not this teach this, what would we say?

Answer: He should be like one who left b'Ones, and he has only four Amos. Therefore, our Mishnah needs to teach that he has 2000 Amos in every direction.

(R. Chunah): (If he was still inside the Techum, it is as if he never left.) This is if four Amos of the Techum of Tiverya overlap the Techum of Magdelah (e.g. if he went from Tiverya to Magdelah).

(R. Chunah citing Rav Ada bar Achavah and R. La citing Reish Lakish): Even if he went [out of his Techum] to Magdelah (e.g. the Techumim meet without any overlap), and returned, it is as if he did not leave.

Question (R. Yeshua of the south): Is this [Heter to return] only for one who left b'Shogeg - or is it even if he left b'Mezid [without a Heter, and a need arose and he saved]?

Answer (R. Pinchas - Mishnah): Anyone who leaves the Techum to save may return to his place. (This comes to include one who left without intent to save!)

Rejection: [The inclusion teaches that] they may return even with their weapons.