Have you ever seen what happens to a fish out of water? It dies right? Same goes for the Heart. If a person doesn't perform thikr, then his/her heart will die and he/she will have no Imaan. Keep doing thikr insha Allah.
A true believer does not have any doubt in Allah assisting him, and that Allah's help is coming forth even if it is after some time. "So do not weaken and do not grieve, and you will be superior if you are [true] believers" (3:139).