"... the West Midlands paid in £3.55 [to the EU] for every pound it gets back [in European grants]" — Open Europe Director Mats Persson, giving evidence in Parliament to the Communities and Local Government Committee, 2012.
Not that it'll have to be replaced, as the funding to 2019 looks fairly secure (due to the way that EU funding rounds operate). We're anyway unlikely to exit fully until spring/summer 2019.
Keep in mind, also, that we probably wouldn't have got another tranche of £157m for 2020-27 — the EU would have shifted ever more funding over to Eastern Europe after 2020, regardless. We'd have been lucky to get a measly £60m for 2020-2027.
Of course, the government (at various levels) will also need to reassure about match-funding and other similar provision. But, understandably, it's doubtful they'll be in a position to give assurances on that point for some months yet.
Update: The EU funding body (Special EU Programmes Body or SEUPB) today said it is "business as usual" for our EU funding application bids, so we can still get and apply for EU funds that run to 2020. (We're likely to finally leave in June 2019).