Theres only been a little bit of research around it but there's evidence that shows that especially short term, team performances improve when a coach is fired and a new one comes in. Happens semi regularly in the NRL
The question is what is a reasonable alternative though.
None of the assistants seem like good candidates and Larkham is clearly the only one you could consider making the interim coach. Would that be a good idea?
White and Johnson have supposedly put their hand up but neither would do it without longer tenure being offered. If one of them would be your desired candidate to appoint in 2020 then sure, but if not, are you locking yourself in to a coach you don't actually want long term just because that's what's needed to sign them now?
I think Johnson is a more palatable appointment than White. What do you do with assistants though? Will new assistants of choice be available now or will they be substandard? Would forcing a new coach to work with the current ones be detrimental?
It's a tough decision. My personal feeling is that things are a basket case now but making a change now will cost a lot of money and probably won't achieve much for the RWC next year. A new appointment should only be made if they're considered the preferred option from 2020 onwards regardless of what happens next year.