I actually dont think its a major problem (the recent retirements). Apart from the young wellington outliers, it is people retiring at an age i would exoect.
It was much worse 10 or so years ago when players were retiring in late 20s -e.g. Brooke Walker etc
We've had a few retirements of domestic legends the last 2 seasons; Cumming, Sinclair, Mason, Marshall. But for me, who had started to get used to the late 20s retirements, the fact we had such a huge number of experience and accomplished old pros on the circuit the last few years means that it has changed for the better.
The domestic contracts/retainers has IMO been one of the best changes by NZC in that last decade. IMO domestic cricket has gotten so much stronger than the late90 /early 00s because of this. And what happens in domestic cricket will flow into the national side about 5 years later. I'm quite positive about improvements to NZ domestic cricket (contacts, pitches) flowing into improved Blackcaps performance over the next decade.
It is a bit of a problem though, don't know how it is 'solved'. I genuinely do wish our domestic players were paid well. The retainers sometimes make their salaries look worse than they are as the retainers are published but the appearance fees don't get often reported and it is harder to try and add up/estimate how much they are paid.
It is a great opportunity for guys who are students, might take a little longer to complete a degree though.
Earlier than this pro and semi-pro eras - say up to the early 90s - when NZ domestic cricket was basically amateur and the season shorter it wasn't much of a problem, players hung around. But the season is now professional length but semi-pro wages.