Fanny died in 1868, aged 24. I agree, Lewis Alford is not in the 1871 census and I think he probably did go back to South Africa. He is in the 1891 census, living at his final address of 2 Westbourne Terrace with his sons Henry and Charles. I note that Florence is using her maiden name!
Peter Turner Wills was also born in Devon, like Lewis, so I think that's their original connection. His father was a farmer. Like Lewis, Peter was a draper's assistant (1851 census)! I wonder if they worked in the same shop. He was in Dorchester in 1851. 1861 he was calling himself a 'Cape Merchant' and lodging quite modestly in Deptford but 10 years later he is living in Blackheath, having married Marianne Boon, Fanny's sister. The 1860s seem to be the decade where Alford and Wills made their money!