That sounds most unfortunate. Whether the saliva comes back or not depends on the salivary glands. If they get zapped you have a dry mouth for life. In my case my major salivary glands seem to have been avoided because I have a certain amount of saliva. It's much less than normal though.

I just hope your father gets lots of improvement. It's very early days.

As for me, I've come back from four cancer diagnoses for two different cancers over the last 20 years but I've kind of made peace with it. I'm just glad to be alive right now to see my grandchildren and participate in this crazy world.

1996, ovarian cancer surgery + cisplatin and taxol.
September, 2007, SCC of left lateral tongue. Excision.
October, 2009 recurrence in scar tissue, T1NOMO. Free flap surgery from left wrist - neck dissection. 63 year old New Zealander. No chemo, no RT.
February, 2014. New primary in left buccal mucosa. Marginal mandibulectomy, neck dissection, right arm free forearm flap. T1N0M0 but third occurrence and some areas of concern: RT started 8 April and finished 19 May.