It will have been deleted but with a supportive and helpful message to the OP from mnhq.
Threads threatening suicide should not be left running in chat on Mumsnet. There was a consultation between MN and various mental health charities on this subject a few years ago (because, as you can imagine, this issue has come up a few times over the years) and their advice was to delete and urge the poster to get real life help.
There is no way MN can stop a random poster from popping up and saying something awful like "go on then, no one will miss you" or whatever. A public forum with anyone and everyone able to see every single thread is NOT the place to turn for support in desperate circumstances. And individual Mumsnetters should not be encouraging it by hand-holding. Imo.