For the love of order
The initial casting works as described. If there is a successful dispel check, then the spell is suppressed for 1d4 + (amount check beat DC) days.
IP invested in this spell is permanently invested, as with the material components of other spells like Restoration. The IP cannot be dropped. The IP cannot be reduced by any mechanic that avoids or reduces material component costs. Recasting to increase caster level is free of IP cost.
Disjunction automatically suppresses the spell, since the description of Disjunction says that it ends the spell as Dispel Magic does. Since Disjunction does not involve a caster check (and is six levels higher than Dispel Magic), the caster level check roll is assumed to be a natural 20 for calculating the duration of the suppression (minimum 1d4+1 days).