Originally posted by Andrew Hudson
The Irish Nationalist Party was still holding its own until conscription came in.
The British government did not impose conscription in Ireland.
The Irish Nationalist Party was losing by-elections to Sinn Fein in 1917:
3 March 1917: North Roscommon
10 May 1917: South Longford
10 July 1917: East Clare (won by Eamon de Valera)
10 August 1917: (won by William Cosgrave).
If there had been no Easter Rising the Irish Nationalist Party would still have lost heavily in the general election held on 14 December 1918 because of the conscription crisis, though it would have done better than in OTL. In that election 25 Sinn Fein candidates were elected unopposed.
Without the Easter Rising and if the British government had not tried to impose conscription in Ireland in 1918, the Irish Nationalist Party would still have lost seats compared with December 1910, but I expect it would have done considerably better than in OTL, possibly winning a majority of the 79 seats in Ireland not won by the Unionists.