Be careful with going with your employer and reassessing at a later date. I'm in a similar situation myself where I'm not too happy with my employer and don't want to tie myself in for much longer. I initially thought I could get PR then leave whenever I like. This is not true. I read from the immigration website that if you leave your employer who has sponsored your PR within the first TWO years, your visa will be cancelled. The employer must let immigration know if you cease employment. I'm not sure if that's a new rule or has always applied but I found it May 2017.
On another relevant note - I myself am looking to apply for my Partner Visa from my 457 which ends late 2018. I thought I could apply for Partner Visa, leave my employer and I would have full working rights on the bridging visa A (BVA) until a decision was made. This is also false. Your BVA is given immediately but only comes into effect when your current visa expires. If you cease employment with the 457 employer, your bridging visa will be void and you will become an unlawful citizen. You can then apply for an emergency visa but you are not given work rights.
Hope this helps a bit.. we seem to be in a very similar situation. I think stick it out with your current employer and get your partner visa submitted asap.
