Nahed,
The current accepted practice is that 'all right' should always be used in formal writing, never 'alright'. For 'formal' you can include novels, short stories, etc. You raise an interesting point about dialogue spelling. However, dialogue is still 'formal' if it appears, say, in a novel. You would only change the spelling of dialogue words if it was absolutely necessary for pronunciation reasons. But just because someone might be speaking in a modern voice, you shouldn't change the spelling when the sound is the same (as in 'alright' and 'all right'
. For example, you wouldn't have a character say, "What are you doing tonite?" or "C U l8r" (excuse me, my text language is non-existent), even if they might think like that. And you're right to consider what editors/agents will consider good or bad written English. On the whole, they are very wary of trendy spellings, mainly because they date so quickly.
Terry