Answer: In the name of Allah, Most Compassionate, Most Merciful,
Assalam’aleykum, I pray this finds you in the best of states.
Jazakum Allah khayr for your question!
Yes, any prayer without sending the Prophet’s blessings (Peace and blessings be upon him) during the last sitting is valid because this action is not from the prayer’s integrals (Arkan/Fard).
Nonetheless, leaving it continuously without excuse is a minor sin because this action is from the prayer’s emphasized sunna.
[Maraqi Al-Falah; Radd Al-Muhtar]
And Allah knows best.
May Allah Most High grant you the best of this world and the next. Please keep us in your du’as!
[Ustadh] Sufyan Qufi