Or at least only one of the lines would have closed.
Looking at an old map, Leigh had two main railway routes through it, and I get the feeling it would have been the Atherleigh railway one that would have closed, and Eccles - Walkden S - Leigh - Wigan remaining open.
More complex than that. There were:
1. Manchester - Eccles - Tyldesley - Springs Branch - Wigan
2. Tyldesley - Leigh - Kenyon Junction (for Liverpool / Warrington Bank Quay, etc.)
3. Kenyon Junction - Pennington - Westleigh - Atherleigh - Bolton Great Moor Street.
4. Some distance from the town centre, Glazebrook - Wigan Central branch.
5. Plus various connections around Pennington / Plank Lane, mainly used for freight, but in early years had a very restricted passenger service between Leigh & Wigan North Western
Leigh suffered somewhat in the pre-diesel era, as you often had to change at Tyldesley to get to Manchester (Exchange). With dieselisation, there was a mostly hourly dmu service from Liverpool & Newton Le Willows to Leigh, Tyldesley, Eccles & Manchester (Exchange). Area was still affected by mining subsidence, so trains were slower than ideal, but from what I remember, patronage increased after dieselisation.
I also wonder if the closure decision was influenced by a desire to avoid the cost of building a bridge near Eccles Junction when the M602 /62 was being built ?
Tyldesley - Wigan suffered steady reductions in passenger services in the years up to closure. Although it passed through well-populated areas, much of the housing lay parallel to the railway, making it difficult for stations to be located where they served the greatest concentrations of population.