You should note, most of these rules are a bit fuzzy. First and foremost, you should go with what your DM says, especially since the magic item has it's own story and personality (and so it might have it's own special abilities with regards to controlling your character, altering your perceptions, etc). As I see it (and I may be wrong):
1. It's unlikely that the mace would dominate you and then not force you to do something. The primary cause of personality conflict isn't being a different alignment; that causes the level loss. Rather, the ego vs will battle comes about when you act in opposition against the weapon:
If the character who possesses the item is not true to that alignment’s goals or the item’s special purpose, personality conflict—item against character—results.
My argument is, that being untrue usually refers to an action; in this case, seeing a cleric and not working to harm them, or doing a good deed, etc. So if the mace was just going to let you go about your business, there'd be no will save.
If the mace did exert its will in such a situation, for that action and for subsequent actions for the rest of the day, you'd essentially be acting against your own will. Since neither intelligent item ego domination nor the Dominate Person spell wipe the subject's memory, you'd be perfectly aware of what you'd done, and how you felt while doing them. Generally, though, you don't get a mental alert when you fail
a will save (e.g. illusions), so it'd be a question of how you perceive your own actions and motivations, which there aren't really concrete rules for.
For example, you might not initially realize what
you'd been forced to do; if the mace's personality was very subtle, it might get away with having you, say, defend a certain person being accosted in a street. Since you don't know that that person had actually just killed a bunch of clerics, and was gonna do it again soon, you get off feeling good about yourself for protecting somebody, and the Mace gets away with harming clerics and being evil. In this case, it's not entirely clear when, if at all, a personality conflict would arise; it's possible, for example, that the mace would stop you from casting Detect Evil on the person. You'd be perfectly aware that you hadn't cast the spell, but it's imaginable that you wouldn't know why. It's possible some kind of Sense Motive check would reveal what the item was doing to you; theoretically, you and the mace should be on speaking terms of some sort (empathy, at the very least), and so it would have to conceal its motivations from you.
Similarly, if you walked up to a healer and bashed him in the head, you'd have no doubt that that was an evil act, and not the sort of thing you generally do. Whether you'd figure out that you'd done so because of the mace, however, is a bit unclear due to the rules being nonspecific. It doesn't say you'd be unaware
that the mace had made you do it, so maybe the mace would get a bluff check? It can have skill ranks in Bluff and it should have a charisma score, and if it's a trapped sorcerer, that score might be pretty frighteningly high. But that'd be up to your DM; there's not exactly a "sense who's enchanting me" skill. Actually, spellcraft might let you do something similar. In any case, it's not explicit anywhere that I know.
So overall, you'd never really be in doubt as to what you'd done, but you might be in doubt as to why exactly you'd done those things, and you also might not realize the full implications of your actions, implications your mace might know full well.
On the second part; yes, if you lost all cleric casting abilities, you'd know that something was wrong. Barring special circumstances, you wouldn't immediately forget your previous spellcasting abilities, and if you have any Knowledge(religion), you'd be aware that clerics who offend their deities often lose spellcasting; it wouldn't take a rocket scientist to piece the two parts together.
2. If you succeed on a will check against the item (again, assuming it's no more than an Intelligent Item, i.e. not a relic or something special-made by your DM), you'd be free to do whatever you wished with the thing. It wouldn't be prevented from communicating with you, so it might try to convince you that it shouldn't be dropped, but beyond argumentation it would hold no sway. It seems like the personality conflicts trigger each time you or the item is forced to act against it's nature, so for example you might have better luck throwing it off a bridge (1 action, so 1 check) rather than, say, putting it up for auction, where each step in the process (finding an auction house, bringing it to auction the day of, physically handing it to the buyer, etc.) might cause another conflict, and thus another check.