I searched for a death in Scotland for Kathleen Weir born 1879 +/- 5 years, from 1930 to 2012 but found no matches. It doesn’t appear she died in Scotland. I can't see a death for her in Carlow either, though the on-line records only go up to 1958.
If he was head of household, the Scottish property Valuation records for the address where John lived might reveal how long he lived there. They cover every year and are held in the National Records of Scotland (NRS) Office in Edinburgh. (They are being put on-line on the Scotlandspeople site but at present 1915 is the latest year so no use in this case.). However you could look up later records in person in Edinburgh or get a researcher to do it for you.
What was John’s occupation when he died? I see from the 1901 census that he was a dentists apprentice. Did he qualify as a dentist? If so, and he was a dentist in Scotland, some professional body might have a record of when he started work there. I have no idea whether they are the correct body but the BDA (Scotland) may be able to direct you:
Have you considered checking to see whether he left a will, and if so who was mentioned in it? Scottish wills for deaths in 1930 are not on-line but are held in the relevant Sheriff Court. (Probably Glasgow in this case if that’s where he died). The registers of confirmations (the Scottish equivalent of Probate), which would confirm that, are held in NRS in Edinburgh. Or you could try e-mailing Glasgow Sheriff Court and asking them if they hold the will giving obviously date and place of death etc.