[SQL] SQL Server... Union all on two IF conditions

I have two table valued functions which I need to do some selects... I was trying to do UNION on that selects but I can't do "union all" to my IF... It should return one row and two columns each if condition...

This code should return:

September | 50

October | 33


how can I do this?!

this was my code:

IF (select TotalTreinos from dbo.tbl_CALCULA_TREINOS_MES('20160901','20160930',2,5)) = (SELECT Presencas FROM DBO.tbl_CALCULA_PRESENCAS('Setembro',9,2))
SELECT 'Setembro' as Mes, 100 AS PercentPresencas
else
select 'Setembro' as Mes, (((SELECT Presencas FROM DBO.tbl_CALCULA_PRESENCAS('Setembro',9,2)) * 100) / (select TotalTreinos from dbo.tbl_CALCULA_TREINOS_MES('20160901','20160930',2,5))) as PercentPresencas

union all

IF (select TotalTreinos from dbo.tbl_CALCULA_TREINOS_MES('20161001','20161031',2,5)) = (SELECT Presencas FROM DBO.tbl_CALCULA_PRESENCAS('Outubro',10,2))
SELECT 'Outubro' as Mes, 100 AS PercentPresencas
else
select 'Outubro' as Mes,(((SELECT Presencas FROM DBO.tbl_CALCULA_PRESENCAS('Outubro',10,2)) * 100) / (select TotalTreinos from dbo.tbl_CALCULA_TREINOS_MES('20161001','20161031',2,5))) as PercentPresencas

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