It'd be a challenge to prosecute murder without physical evidence - I think the search of the property is LE's best chance to find something, so they're not going to leave any stone unturned.
I think most murderers are reluctant to move a body if they have access to an easy/secure place to bury it: so much more risk of being seen, or someone coming across remains while walking their dog, or a weighted body coming loose and floating after a while. In a case like this, the carers having failed to report her missing, if her body had been found, the carers would be the obvious suspects. It seems to me that if they'd wanted to dispose of something, the property would give them so much more time, privacy, security, especially when they had (from facebook) a big aggressive dog to keep people away.
In terms of other evidence, there may be many people, who haven't spoken to the media, who could provide a lot more info. For example, AJ's family, who don't seem at all close, but who surely knew about Margaret? I think by collecting all the info from multiple sources, it could be possible to find a timeframe when circumstances changed and lies began.