How much of a view is persisted when you create an index?
All three columns are persisted to disk in the clustered index on the indexed view (no different, really, from a clustered index on a regular table). You can validate this using DBCC PAGE. I created the following structure in tempdb:

USE tempdb;
GO

CREATE TABLE dbo.a(a INT);
CREATE TABLE dbo.b(a INT, b DATETIME);
CREATE TABLE dbo.c(a INT, c CHAR(32));

INSERT dbo.a SELECT 1;
INSERT dbo.b SELECT 1, SYSDATETIME();
INSERT dbo.c SELECT 1, REPLICATE('c', 32);
GO

CREATE VIEW dbo.v
WITH SCHEMABINDING 
AS
  SELECT a.a, b.b, c.c
  FROM dbo.a
  INNER JOIN dbo.b
  ON a.a = b.a
  INNER JOIN dbo.c
  ON a.a = c.a;
GO

CREATE UNIQUE CLUSTERED INDEX x ON dbo.v(a);
GO


Turned a trace flag on so I can use IND/PAGE:

DBCC TRACEON(3604, -1);
DBCC IND('tempdb', 'dbo.v', 1);


Results:



So I knew to check page 312:

DBCC PAGE(2, 1, 312, 3);


And here are the three values from the join, even though they're not all part of the unique aspect of the clustered index: