The right question is - can the A-10 still do is job, in a non very permissive environment, and/or against a competent adversary with decent-ish anti-air weapons?
The answer there is complicated, so bear with me.
The short answer is sometimes yes, sometimes no, it depends.
However in general, specifically for the CAS mission, the A-10 is capable of handling the mission, although it will take losses in early phases against a fully intact air defense network. Note that the nature of CAS means that said network is going to be degrading rapidly, because CAS does not occur in a vacuum.
The primary benefit of stealth is the reduction of detection range. In 'conventional' stealth aircraft, such as F-117, F-22, F-35, B-2, and the upcoming B-21, this is accomplished by reduction in radar cross section and other emissions/reflections. However the older way to accomplish this is to fly extremely low.
All forms of detection against aircraft, be it radar, IR, UV, etc, requires a degree of line of sight. Certain types of radar have, in certain circumstances, non-LOS capability. However, this non-LOS capability is only applicable to extremely large radar systems operating over great ranges where they make use of various properties of the atmosphere to 'bend' radar waves.
So, to reduce visibility to these sensors, you either reduce your signature (the 'Stealth' route) or you keep solid objects between you and the sensors in question.
The A-10 does the latter. It is capable of flying low enough to the ground that LOS is broken by terrain. Moreover, at the altitude the A-10 operates, there is a phenomena called 'ground clutter' which makes even airborne radar have severe issues locking on to a target.
As I explained earlier in the thread. The A-10 makes brutal use of ground clutter and terrain in its attack profile. By keeping extremely low, terrain itself will mask the approach. The A-10 will have the benefit of datalinks back to AWACS and various ELINT birds informing the pilot of the location of targets and threats.
The A-10 pilot will therefore already know where his target is with a solid degree of confidence. In a CAS run, he'll either be making a rapid pass and deploying retarded bombs, lofting Maverick (which can take advantage of off-platform designation, I might add) without breaking cover, or perform the pop-up and dive attack affectionately known as BRRRTTTT.
So now your air defense platform needs to perform the following actions in the sub 3 second span that the A-10 is vulnerable.
Detect the target.
Identify the target (would really suck to waste your ammo on a flock of startled birds, wouldn't it)
Track the target (it's a moving target, you can't shoot where it is now, you need to predict where it will be in 1 to 2 seconds when your shells will intersect)
Engage the target.
Meanwhile, BRRRRTTT is heading your way, which is what the Chieftain would describe as a 'significant emotional event'.
Note, that even with all of this, there's still guesswork. Because that A-10 is not going to fly straight. It's going to break, either left or right. Flip a ruble, Ivan, because if you guess wrong you'll still miss.