Q:

How does the conversion of Hoekse Lĳn to Metrolĳn B affect Rail & Sail tickets?

The Stenaline Rail and Sail ticket covers travel from London to any train station in The Netherlands, including the train and the ferry crossing from Harwich to Hoek van Holland.  However, from 1 April 2017, there will be no more trains from Hoek van Holland to Schiedam, as the Hoekse Lĳn is being converted to a metro line.  During the conversion, there are rail replacement buses.
Currently, Rail & Sail tickets are not valid on the Rotterdam metro network.  I assume they will be valid on the rail replacement buses and on the metro line opening late 2017.  Is this officially confirmed by Stenaline or RET anywhere?  Exactly on what RET lines will I be able to travel with a Rail & Sail ticket?
According to seat61, rail tickets will be valid on the buses.  But this is contradicted by RET, which states NS-reisproducten zijn niet geldig bij de RET, which means that NS travel products are not valid at RET, contradicting seat61.

A:

Passengers will receive a Combi-Ticket NS-RET:

Combi-Ticket NS-RET.  Valid on all busses (sic), trams, and metro operated by RET.  All trains operated by NS.  Not valid in busses (sic), trams, trains and metro operated by other public transport operators.  Supplement required for Intercity direct and ICE.  Not valid in Thalys and RET BOB-bus.  Check-in and out required with each carrier.
Information from RET (posted after the question was asked):

Stena Line passengers can use bus line 711 to travel direct to Schiedam Centrum station.

(...)

Travel products for Stena Line passengers

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Travel products for Stena Line passengers
  RET – NS Combi-Ticket : valid for RET and NS

(...)

Where are these travel products on sale?
  RET – NS Combi-Ticket:
  - On board Stena Line ships
  - Online or by phone as part of a 'crossing + public transport' package 

(...)

How do I get my NS-RET Combi-Ticket if I buy it as part of the 'crossing + public transport' package?
Customers in the Netherlands, Belgium and Luxembourg:
The NS-RET Combi-Ticket will be sent out approximately 4 weeks before departure by Stena Line, provided payment has been received for the package and the ticket is part of the reservation. You will not receive separate train tickets for the part of your journey in England. Your printout of your Stena Line confirmation will also serve as your train ticket. For bookings up to 8 days before departure, NS-RET Combi-Tickets are sent out immediately after payment.
Customers in the United Kingdom:
  Stena Line hands the tickets to UK customers in Harwich on the day of departure; so in the UK, no tickets are sent out by post but instead passengers receive them at check-in on board, provided payment for the package has been received and the ticket is part of the reservation. You will not receive separate train tickets for the part of your journey in England. Your printout of your Stena Line confirmation will also serve as your train ticket.  

More details on terms and conditions for NS-RET Combi-Ticket.

