I find that Japanese texts use a lot of abbreviations that aren't explained in grammar books. I need some help from /jp/...

verbs ending in -kya: I don't know if this is a substitute for "-kereba", but it seems that way. I hope somebody can confirm. for example: 戻らなきゃ (modoranakya, if we don't return?)

verbs ending in -chimasu: it looks like this means the same as "-te shimau", again I hope you can confirm. 来ちまった (kichimatta, I came/arrived?)

"kede", I definitely can't tell if this is an abbreviation or what. I couldn't find the word anywhere. For example: 命がけで伝えたくれた (inochi ga kede tsutaeta kureta, X saved my life?)

If you know of a site which gathers more of these abbreviations, I'd appreciate a link, so I don't have to go lurking and asking around. Thanks in advance.