Sure! Here are the rewritten sentences:

1. His father hasn't smoked cigarettes since he was seriously ill.

2. Her sisters haven't eaten too much fast food since they had trouble losing weight.

3. It hasn't snowed here in six years.
It last snowed here six years ago.
It is six years since it last snowed here.

4. It hasn't been since last summer that Mary wrote to me.
It last summer that Mary wrote to me.

Here are the rewritten sentences:

1. His father stopped smoking cigarettes when he was seriously ill.
- His father hasn't smoked cigarettes since he was seriously ill.

2. Her sisters gave up eating too much fast food when they had trouble losing weight.
- Her sisters haven't eaten too much fast food since they had trouble losing weight.

3. The last time it snowed here was six years ago.
- It hasn't snowed here for six years.
- It last snowed here six years ago.
- It is six years since it snowed here.

4. Mary last wrote to me last summer.
- It hasn't been since last summer that Mary wrote to me.
- It last wrote to me last summer.