I had this happen recently, and sorry if my memory is fuzzy, but I was not expelled, but suspended. I didn't have to rejoin the thief guild, I think... After my week was up I could keep on stealing as I had before. Unless my memory fails me.Being reported for murder whilst a member of the Thieves Guild will result in summary expulsion, and you will not be able to rejoin for at least one week.
Anyone else have a more recent experience and a more reliable memory?
If anyone would like to murder one of my characters to test this out, send me a PM and we can arrange it