@DuchessofReality
This is a really good question.
You don't mention how old your DS is?
Is he between 5- 11 or older than 12 years?
Salbutamol DOES still have a place in the management of some asthma, specifically acute, severe and "brittle" asthma, where there can be sudden, life-threatening, severe attacks that come from nowhere, with no triggers or precipitating factors. And it is still used in children under hospital care, it has a place, for sure. It can be life-saving, as I've mentioned in previous posts. It won't become unavailable, just prescribed an awful lot less, because of the risks of over-using it, and that it can "mask" severe, underlying inflammation.
As you say, your DS will hopefully, and probably, need his SABA, ( aka, Short-acting broncho-dilator, Salbutamol or Ventolin) a lot less as time goes on, as the protective anti-inflammatory effect of the inhaled steroid takes effect and dampens down his irritable, twitchy airways. However, I absolutely understand your nervousness about the prospect of not having Salbutamol to hand in an asthma crisis. Depending on how unpredictable your DS's asthma symptoms are, I would imagine his consultant would be recommending you keep it, and in the event of an emergency, 8-10 puffs, over 5 minutes, via a spacer is still what to do, while waiting for an ambulance. You really need to clarify this with his consultant. I would hope he/she has discussed a PAAP ( Personalised Asthma Action Plan)? This should cover everything from day-to-day management of his asthma with his prescribed medication and devices, to crisis management, and everything in between, ( for instance, how to deal with P.E at school or other activities). You should make lots of copies of this, ( a good one will have pictures of his asthma devices, ie, brown/red inhaler, what his particular spacer looks like) and make sure everyone has a copy, teachers, school, wrap-a-round care, after-school activities, Cubs/Beavers etc...
During this time, your DS's consultant will be vigilant as to how his asthma has been, ie, how many times as he needed extra maintenence doses ( Symbicort), what were the triggers, did he need a short course of oral steroids, any hospitalisations etc...?
With his Symbicort, this can be used for in-between doses, again, depending on his age?
But an extra 6-8 puffs daily, so for instance, if he were to get a hay-fever flare, on the back of a virus, if he is allergic to pet dander...You can fo this for a couple of days if he is "tight", wheezing or coughing more, especially at night.
But, and this is important! It isn't used for crisis management where, as I mentioned above, Salbutamol would be used. But, extra doses in the run- up to a potential crisis for a few days might well avert the crisis and need for this. Which is why diligent use of regular inhalers/medication is SO important...lack of symptoms indicate well-controlled asthma. But regular reviews are also important in whether it might be appropriate to "step down", asthma ebbs and flows over a lifetime, so its as important to step down, sometimes as to step up.
But you really need to speak to his consultant and get this all written down clearly, as it is highly personalised, for each individual, as to how to manage their asthma.
I do hope his symptoms reduce. Most people, with good asthma management, appropriate medication and clear explanation should be able to live life normally, including athletes and people doing high-performing activities. But, and I would urge you again, do speak to his paediatrician for written clarification.
All the best. It's horrible, having a child with asthma; I had one myself and one is constantly alert and vigilant. I completely understand your worry.