You are asking the wrong question.
The best question to ask is "How much less will it cost me this year? "
€100k @ 0.35% is €350 per year.
With your question, you are mixing up euros at 2014 values with euros at 2044 values. That is like adding 350 grapes to 350 melons and getting an answer of 700.
You could ask a more complicated question: If I make the Bank of Ireland payments to KBC, how much time will I knock off the mortgage. But even that is a very hard concept to understand.
If someone is choosing between two houses to rent, they don't say House A will be €30,000 cheaper over 30 years. They say that House A is €1,000 cheaper per month.
With a mortgage, you are simply renting money. The longer you rent it, the more rent you pay.
Brendan