Hopefully they'll turn up and all will be well. However, to protect your interests you may wish to consider the possibility that it could be deferred again (and again), and the further possibility that when the pre-install team do eventually arrive, they may find an obstruction, blockage or access permission problem that makes connecting you uneconomic for VM, in which case your install, and your order will be cancelled.
Given that possibility of further delays or cancellation by VM, does that make a difference to what you would do now? If you're living with an adequate "backup option" of surviving on mobile date, you might choose to sit it out. Alternatively you might want to avoid further problems with VM, cancel the order and get an Openreach connection back on.
VM have some attractive new customer offers; Speeds are for most customers high, and consistently delivered. Wireless capabilities of the hubs are mediocre, but adequate for undemanding circumstances. But when any thing happens that requires contact with the company, or the company makes promises that "event X will happen by date Y", the customer experience is often exceptionally disappointing, and putting things right can sometimes take months. Make any decision wisely.