Switching employer flowchart : Does it still work 4 years later?

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I read this flowchart before (but it is dated 2014) and I am thinking about switching to another employer.
I am going to paste it here as well to make it easier

1. Get a conditional offer letter from the new employer. Read it thoroughly and make sure everything is right.
2. Ask the new employer to generate a CoS (certificate of sponsorship). Once generated, read it thoroughly and make sure everything is right. IIRC, this would be an unrestricted COS right?
3. Once you have your CoS number, make a fresh Tier 2 application. You will not have to show funds or proof of English if you were already on a Tier 2 Visa.
4. Wait for your new BRP to arrive.
5. Once you have the new Visa, ask the new employer to draft a final UNCONDITIONAL offer letter with a start date that corresponds to the notice period that you have to give to your current employer. Preferably, start from the beginning of a new month.
6. Proofread your final contract and sign it. Ask your new employer to report via SMS (sponsorship management system) that you are currently completing your notice period. Why is this step about SMS needed?
7. Once all the above are done, immediately let your old employer know and start the notice period.
8. Complete your notice period and then join your new job!

My main question is that, if the start date on COS can only be 3 months away, and a normal switching timescale is 8-12 weeks, given that I have to give 2 months notice, does that mean I would have to choose the priority service/premium to speed things up?

If, touchwood, the application fails, would I lose the original visa? I have read on the forum it happened to someone even though it isn't supposed it. I can't find that thread anymore so couldn't follow the story unfortunately.

Thanks!

Has anyone done this recently would be able to share?