Is the repentance of disputants who do not speak to one another accepted, and is one of them saying "Peace be upon you" sufficient for reconciliation?

Firstly, it is not permissible to abandon a Muslim for more than three days, with the exception of abandoning a person who commits a sin for a beneficial purpose. Abandonment ceases with a salutation (greeting of peace).

Secondly, Allah accepts repentance at all times, except at the time of the death rattle (ghargara) or the sun rising from the West. Repentance has three pillars: ceasing the sin, regretting it, and resolving not to return to it. If one repents from a sin while still committing another, their repentance is valid.

As for the Hadith about deferring forgiveness for those who harbor grudges, it does not mean that the repentance of the one who harbors grudges for their other sins is not accepted.