It's essentially impossible to know the "lifespan" (depending on what exactly you mean by that term) of the H125 helicopter. Since, as the source below indicates, the longest H125 in service is 45 years, it's probably reasonable to conclude that its "lifespan" will be somewhat more than 45 years.
As a practical matter, the lifespan of any aircraft is based on, among other things, being properly maintained, the availability of parts, maintaining a competitive operating cost compared to similar aircraft can be operated, etc. Some aircraft have continued in useful service for many, many years.
An Airbus H125 (formerly an AS350) has been in service at least 45 years according to this source.