I'll venture an opinion. I don't believe the heat from a properly done weld will have any detrimental effect on sound damascus. The issues with welding generally have to do with higher carbon steels and alloys; some are real fussy about rod, temperature, previous heat treat, etc.

Were higher carbon steels ever used with lower carbon/iron in making damascus? I think this could have been a problem for the welders/blacksmiths of old. I'd guess any heat treatable steel would have been in annealed state after welding into damascus.

DDA