Will Allah forgive one who intended disbelief once due to waswasah (whispers/insinuations from Satan) and verbally abused Allah by mistake, and is now remorseful and afraid, even though Satan whispers to him that Allah will not forgive him because he disbelieved?

You are not to be held accountable for a statement or action that occurred under the influence of waswasah (whispers of Satan/obsessive thoughts), because you are, in essence, compelled. You have not, in fact, committed disbelief because of these waswasah. Repentance from all sins is accepted. Be easy on yourself, cast away the waswasah, and strive against them. You will be rewarded for resisting them and for striving to rid yourself of them.