Proper is a very flexible word 
But a great excuse for a random rant! :
Generally, wood never dies until it is consumed by something .. it has a specific structure that reacts to various environmental signals.
The reaction will depend on the species of wood - the most obvious reaction is movement.
If that movement is too sudden (in wood-time) then the fibres might part company - i.e. crack.
If it is slow enough, the tensions are adjusted according to the species response process.
For instance, boxwood has a strong movement response and is very good at re-adjusting to movement - the flutes in museums are notorious for crawling off the display shelf. Like most wood, boxwood responds to humidity.
I had a piece of Cambodian ebony that responded to sunlight .. behaved in peristaltic waves.
In tonewoods, the primary motive to move is humidity - so the trick is to slow it down to wood-time.
Hence we swab and oil.
Swab is the most urgent measure - water in the bore .. well .. that’s over 100% humidity and will get in through everything eventually .. the oil slows this down long enough to play the whistle for a bit.
But if you put away a wet whistle, there’s a good chance it won’t be a whistle when you come back for it.
If you forget to oil, then the whistle might stop being a whistle mid-tune. It’s all about timing.
Another factor to consider is air temperature. Cold air is very dry - even at 100% humidity, much dryer than warm air.
Cold nights kill a lot of whistles - here’s why:
When you warm-up a whistle, it will comply to the ambient humidity of your breath - i.e. near 100%.
The interior of the whistle becomes a micro-climate. If it is laid down, the internal microclimate quickly rebalances with the ambient climate - all the moisture goes out in a rush. The wood will dance chaotic arabesques according to its nature.
Only a bit of oil will keep this dance civilised .. wild things are great, but not always appropriate. .. for example, goats like to climb onto humpy-shaped cars .. like Volkswagens .. (the old sort)
Special note for oil - some oil interferes with the natural wood oils - and very thin parts of the instrument (edge of sound-blade) can become de-natured (turn to jelly) over time, if the ramp gets too much oil.
Avoid oils that encourage colonies of bacteria or mould.
Vitamin E is a good additive for natural oils such as almond or walnut - as an additive, sandalwood oil is even better(it’s a natural disinfectant).
Good old light-grade machine oil is OK as well . if you are OK with petrochemicals.
I’m not .. but then .. I also don’t shave ;{>
(edit: damn .. forgot to use the word “goat” .. thank the Borg for post-temporal revision!)